Control system and method for multiple parallel desalination systems

ABSTRACT

Embodiments described herein generally relate to humidification-dehumidification desalination systems, including apparatuses that include a vessel comprising a humidification region (e.g., a bubble column humidification region) and a dehumidification region (e.g., a bubble column dehumidification region), mobile humidification-dehumidification (HDH) desalination systems (e.g., systems having a relatively low height and/or a relatively small footprint), and associated systems and methods. Certain embodiments generally relate to methods of operating, controlling, and/or cleaning desalination systems comprising a plurality of desalination units (e.g., HDH desalination units).

RELATED APPLICATION

This application claims priority under 35 U.S.C. §119(e) to U.S.Provisional Patent Application No. 62/339,805, filed May 20, 2016, andentitled “Control System and Method for Multiple Parallel DesalinationSystems,” which is incorporated herein by reference in its entirety forall purposes.

TECHNICAL FIELD

Embodiments described herein generally relate to ahumidification-dehumidification (HDH) desalination system, which inspecific embodiments may be a bubble column HDH desalination system, andmethods of operating, controlling, and/or cleaning desalination systemscomprising a plurality of HDH desalination units.

BACKGROUND

Fresh water shortages are becoming an increasing problem around theworld, with demand for fresh water for human consumption, irrigation,and/or industrial use continuing to grow. In order to meet the growingdemand for fresh water, various desalination methods may be used toproduce fresh water from salt-containing water such as seawater,brackish water, water produced from oil and/or gas extraction processes,flowback water, and/or wastewater. For example, one desalination methodis a humidification-dehumidification (HDH) process, which involvescontacting a saline solution with a carrier gas in a humidifier, suchthat the carrier gas becomes heated and humidified. The heated andhumidified gas is then brought into contact with cold water in adehumidifier, thereby producing pure water.

However, HDH systems and processes often involve certain drawbacks. Forexample, due to the use of a carrier gas in HDH systems, a largepercentage of non-condensable gas (e.g., air) is generally present,which can lead to relatively low heat and mass transfer rates. Inaddition, the presence of a non-condensable gas in a dehumidifier canincrease the thermal resistance to vapor condensation on a cold surface,thereby reducing the effectiveness of surface condensers. HDH systemsmay, additionally, require relatively large amounts of energy tooperate. HDH systems with improved properties such as, for example,reduced power consumption and/or increased heat and mass transfer ratesin the presence of non-condensable gases, are therefore desirable.

SUMMARY

Apparatuses comprising both a humidification region and adehumidification region, and use of the apparatuses in various heat andmass exchange systems, are disclosed. In another aspect, mobilehumidification-dehumidification (HDH) desalination systems, and methodsof operating, controlling, and/or cleaning desalination systemscomprising a plurality of HDH desalination units, are also disclosed.The subject matter of the present invention involves, in some cases,interrelated products, alternative solutions to a particular problem,and/or a plurality of different uses of one or more systems and/orarticles.

Certain embodiments relate to desalination systems. In some embodiments,a desalination system comprises a vessel comprising a humidificationregion comprising a humidification region liquid inlet fluidicallyconnected to a source of salt-containing water, a humidification regiongas inlet fluidically connected to a source of a gas, and ahumidification region gas outlet. In some embodiments, thehumidification region is configured to produce a vapor-containinghumidification region gas outlet stream enriched in water vapor relativeto the gas received from the gas inlet. In some cases, the vesselfurther comprises a dehumidification region comprising adehumidification region gas inlet fluidically connected to thehumidification region gas outlet, a dehumidification region gas outlet,and a dehumidification region water outlet. In certain cases, thedehumidification region is configured to remove at least a portion ofthe water vapor from the vapor-containing humidification region gasoutlet stream to produce a dehumidification region water outlet streamand a dehumidification region gas outlet stream lean in water vaporrelative to the humidification region gas outlet stream.

In some embodiments, the desalination system comprises a vesselcomprising a humidification region comprising a humidification regiongas inlet fluidically connected to a source of a gas, a humidificationregion gas outlet, and at least one humidification chamber containing aliquid layer comprising an amount of salt-containing water. In somecases, the humidification region is configured to produce avapor-containing humidification region gas outlet stream enriched inwater vapor relative to the gas received from the gas inlet. In someembodiments, the vessel further comprises a dehumidification regioncomprising a dehumidification region gas inlet fluidically connected tothe humidification region gas outlet, a dehumidification region wateroutlet, and at least one dehumidification chamber containing a liquidlayer comprising an amount of water. In certain embodiments, thedehumidification region is configured to remove at least a portion ofthe water vapor from the humidification region gas outlet stream toproduce a dehumidification region water outlet stream and adehumidification region gas outlet stream lean in water vapor relativeto the humidification region gas outlet stream. In some cases, theliquid layer of the at least one humidification chamber and/or theliquid layer of the at least one dehumidification chamber have a heightof about 0.1 m or less.

In some embodiments, the desalination system comprises a vesselcomprising a humidification region comprising a humidification regionliquid inlet fluidically connected to a source of salt-containing water,a humidification region gas inlet fluidically connected to a source of agas, and a humidification region gas outlet. In some embodiments, thehumidification region is configured to produce a vapor-containinghumidification region gas outlet stream enriched in water vapor relativeto the gas received from the gas inlet. In some cases, the vesselfurther comprises a dehumidification region comprising adehumidification region gas inlet fluidically connected to thehumidification region gas outlet, a dehumidification region gas outlet,and a dehumidification region water outlet. In certain cases, thedehumidification region is configured to remove at least a portion ofthe water vapor from the vapor-containing humidification region gasoutlet stream to produce a dehumidification region water outlet streamand a dehumidification region gas outlet stream lean in water vaporrelative to the humidification region gas outlet stream. In someembodiments, the desalination system further comprises a heat exchangerseparate from the vessel. In certain cases, the heat exchanger isfluidically connected to the dehumidification region water outlet andthe humidification region liquid inlet. In certain embodiments, the heatexchanger is configured to transfer heat from the dehumidificationregion water outlet stream to the humidification region liquid inletstream.

According to some embodiments, the desalination system comprises avessel comprising a humidification region comprising a humidificationregion liquid inlet fluidically connected to a source of salt-containingwater, a humidification region gas inlet fluidically connected to asource of a gas, and a humidification region gas outlet. In someembodiments, the humidification region is configured to produce avapor-containing humidification region gas outlet stream enriched inwater vapor relative to the gas received from the gas inlet. In somecases, the vessel further comprises a dehumidification region comprisinga dehumidification region gas inlet fluidically connected to thehumidification region gas outlet, a dehumidification region gas outlet,and a dehumidification region water outlet. In certain cases, thedehumidification region is configured to remove at least a portion ofthe water vapor from the vapor-containing humidification region gasoutlet stream to produce a dehumidification region water outlet streamand a dehumidification region gas outlet stream lean in water vaporrelative to the humidification region gas outlet stream. In someembodiments, a portion of a gas stream is extracted from at least oneintermediate location in the humidification region and fed to at leastone intermediate location in the dehumidification region.

In some embodiments, the desalination system comprises a vesselcomprising a humidification region comprising a humidification regiongas inlet fluidically connected to a source of a gas, a humidificationregion gas outlet, and at least one humidification chamber containing aliquid layer comprising an amount of salt-containing water. In somecases, the humidification region is configured to produce avapor-containing humidification region gas outlet stream enriched inwater vapor relative to the gas received from the gas inlet. In someembodiments, the vessel further comprises a dehumidification regioncomprising a dehumidification region gas inlet fluidically connected tothe humidification region gas outlet, a dehumidification region wateroutlet, and at least one dehumidification chamber containing a liquidlayer comprising an amount of water. In certain embodiments, thedehumidification region is configured to remove at least a portion ofthe water vapor from the humidification region gas outlet stream toproduce a dehumidification region water outlet stream and adehumidification region gas outlet stream lean in water vapor relativeto the humidification region gas outlet stream. In some cases, the atleast one humidification chamber and/or the at least onedehumidification chamber are fluidically connected to one or more bubblegenerators.

In some embodiments, the desalination system comprises a vessel. Incertain cases, the vessel comprises a bubble column humidificationregion comprising a humidification region liquid inlet fluidicallyconnected to a source of salt-containing water, a humidification regiongas inlet fluidically connected to a source of a gas, a humidificationregion gas outlet, and one or more bubble generators. In certainembodiments, the bubble column humidification region is configured toproduce a vapor-containing humidification region gas outlet streamenriched in water vapor relative to the gas received from thehumidification region gas inlet. In certain cases, the vessel furthercomprises a bubble column dehumidification region comprising adehumidification region gas inlet fluidically connected to thehumidification region gas outlet, a dehumidification region gas outlet,a dehumidification region water outlet, and one or more bubblegenerators. In certain embodiments, the bubble column dehumidificationregion is configured to remove at least a portion of the water vaporfrom the vapor-containing humidification region gas outlet stream toproduce a dehumidification region water outlet stream and adehumidification region gas outlet stream lean in water vapor relativeto the humidification region gas outlet stream. In some embodiments, thevessel has a height of about 5 m or less.

In some embodiments, the desalination system comprises a bubble columnhumidifier. In certain cases, the bubble column humidifier comprises ahumidifier liquid inlet fluidically connected to a source ofsalt-containing water; a humidifier gas inlet fluidically connected to asource of a gas; a humidifier gas outlet; and one or more bubblegenerators. In some embodiments, the bubble column humidifier isconfigured to produce a vapor-containing humidifier gas outlet streamenriched in water vapor relative to the gas received from the humidifiergas inlet. In certain embodiments, the bubble column humidifier has aheight of about 5 m or less. In certain cases, the bubble columnhumidifier is configured to evaporate at least about 500 barrels perday. In some embodiments, the desalination system comprises a bubblecolumn dehumidifier. In certain cases, the bubble column dehumidifiercomprises a dehumidifier gas inlet fluidically connected to thehumidifier gas outlet; a dehumidifier gas outlet; a dehumidifier wateroutlet; and one or more bubble generators. In some embodiments, thebubble column dehumidifier is configured to remove at least a portion ofwater vapor from the vapor-containing humidifier gas outlet stream toproduce a dehumidifier water outlet stream comprising substantially purewater and a dehumidifier gas outlet stream lean in water vapor relativeto the humidifier gas outlet stream. In certain embodiments, the bubblecolumn dehumidifier has a height of about 5 m or less. In certain cases,the bubble column dehumidifier is configured to condense at least about500 barrels per day.

Some aspects are related to methods of removing scale from a pluralityof desalination units. In some embodiments, the method comprisesproviding a desalination system comprising a plurality of desalinationunits, wherein two or more desalination units of the plurality ofdesalination units are heat exchanger-containing desalination units thateach comprise a humidifier, a dehumidifier, and a first heat exchangerfluidically connected to the humidifier. In some embodiments, the methodfurther comprises flowing a first fluid stream through a first fluidicpathway of the first heat exchanger of each heat exchanger-containingdesalination unit. In some embodiments, the method further comprisesflowing a second fluid stream through a second fluidic pathway of thefirst heat exchanger of each heat exchanger-containing desalinationunit. In some embodiments, the method further comprises measuring afirst temperature of each second fluid stream downstream of the firstheat exchanger. In some embodiments, the method further comprisesdetermining an average first temperature of all the first temperaturesmeasured in the measuring step. In some embodiments, the method furthercomprises identifying at least one fouled first fluidic pathwaycharacterized by a first temperature measured in the measuring step thatdiffers from the average first temperature by greater than 10% on theKelvin scale. In some embodiments, the method further comprisesselectively flowing a de-scaling composition through only the at leastone fouled first fluidic pathway.

In some embodiments, the method of removing scale comprises providing adesalination system comprising a plurality of desalination units,wherein two or more desalination units of the plurality of desalinationunits are heat exchanger-containing desalination units that eachcomprise a humidifier, a dehumidifier, and a first heat exchangerfluidically connected to the humidifier. In some embodiments, the methodfurther comprises flowing a first fluid stream through a first fluidicpathway of the first heat exchanger of each heat exchanger-containingdesalination unit. In some embodiments, the method further comprisesflowing a second fluid stream through a second fluidic pathway of thefirst heat exchanger of each heat exchanger-containing desalinationunit. In some embodiments, the method further comprises measuring afirst flow rate of each second fluid stream downstream of the first heatexchanger. In some embodiments, the method further comprises determiningan average first flow rate of all the first flow rates measured in themeasuring step. In some embodiments, the method further comprisesidentifying at least one fouled first fluidic pathway characterized by afirst flow rate measured in the measuring step that differs from theaverage first flow rate by greater than 10%. In some embodiments, themethod further comprises selectively flowing a de-scaling compositionthrough only the at least one fouled first fluidic pathway.

Other advantages and novel features of the present invention will becomeapparent from the following detailed description of various non-limitingembodiments of the invention when considered in conjunction with theaccompanying figures. In cases where the present specification and adocument incorporated by reference include conflicting and/orinconsistent disclosure, the present specification shall control. If twoor more documents incorporated by reference include conflicting and/orinconsistent disclosure with respect to each other, then the documenthaving the later effective date shall control.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting embodiments of the present invention will be described byway of example with reference to the accompanying figures, which areschematic and are not intended to be drawn to scale. In the figures,each identical or nearly identical component illustrated is typicallyrepresented by a single numeral. For purposes of clarity, not everycomponent is labeled in every figure, nor is every component of eachembodiment of the invention shown where illustration is not necessary toallow those of ordinary skill in the art to understand the invention. Inthe figures:

FIG. 1A shows a schematic illustration of an exemplary desalinationsystem comprising a vessel comprising a single-stage humidificationregion and a single-stage dehumidification region, according to someembodiments;

FIG. 1B shows a schematic illustration of an exemplary desalinationsystem comprising a vessel comprising a single-stage humidificationregion, a single-stage dehumidification region, a stack, two dropleteliminators, and a liquid collector, according to some embodiments;

FIG. 2A shows, according to some embodiments, a schematic illustrationof an exemplary desalination system comprising a vessel comprising amulti-stage humidification region and a multi-stage dehumidificationregion;

FIG. 2B shows, according to some embodiments, a schematic illustrationof an exemplary desalination system comprising a vessel comprising amulti-stage humidification region, a multi-stage dehumidificationregion, and an intermediate gas injection point;

FIG. 2C shows, according to some embodiments, a schematic illustrationof an exemplary desalination system comprising a vessel comprising amulti-stage humidification region, a multi-stage dehumidificationregion, and an intermediate gas extraction point fluidically connectedto an intermediate gas injection point;

FIG. 2D shows, according to some embodiments, a schematic illustrationof an exemplary desalination system comprising a vessel comprising amulti-stage humidification region, a multi-stage dehumidificationregion, two droplet eliminators, and a liquid collector;

FIG. 2E shows, according to some embodiments, a schematic illustrationof an exemplary desalination system comprising a vessel comprising amulti-stage humidification region, a multi-stage dehumidificationregion, two droplet eliminators, a liquid collector, and an externalsump;

FIG. 3A shows a schematic illustration of an exemplary desalinationsystem comprising a vessel comprising a humidification region comprisinga plurality of vertically-arranged stages positioned horizontallyadjacent to a dehumidification region comprising a plurality ofvertically-arranged stages, according to some embodiments;

FIG. 3B shows a schematic illustration of an exemplary desalinationsystem comprising a vessel comprising a humidification region and adehumidification region, a main internal gas conduit fluidicallyconnected to a main gas outlet of the humidification region and a maingas inlet of the dehumidification region, and an auxiliary internal gasconduit fluidically connected to an intermediate gas outlet of thehumidification region and an intermediate gas inlet of thedehumidification region, according to some embodiments;

FIG. 4 shows, according to some embodiments, a schematic illustration ofan exemplary desalination system comprising a vessel comprising ahumidification region comprising a plurality of horizontally-arrangedstages positioned horizontally adjacent to a dehumidification regioncomprising a plurality of horizontally-arranged stages;

FIG. 5 shows a schematic illustration of an exemplary desalinationsystem configured for batch processing, according to some embodiments;

FIG. 6A shows, according to some embodiments, a schematic illustrationof an exemplary baffle;

FIG. 6B shows, according to some embodiments, a schematic illustrationof an exemplary weaving baffle;

FIGS. 7A-C show schematic illustrations of an exemplary combined HDHapparatus comprising an integrated wheel base, according to someembodiments;

FIG. 8A shows, according to some embodiments, a schematic illustrationof an exemplary combined HDH apparatus positioned on a flatbed shippingtrailer;

FIG. 8B shows, according to some embodiments, a schematic illustrationof an exemplary combined HDH apparatus positioned on a stepdeck shippingtrailer;

FIG. 8C shows, according to some embodiments, a schematic illustrationof an exemplary combined HDH apparatus positioned on a lowboy shippingtrailer;

FIG. 9A shows a schematic illustration of an exemplary system comprisinga humidifier positioned on a first flatbed shipping trailer and adehumidifier positioned on a second flatbed shipping trailer, accordingto some embodiments;

FIG. 9B shows a schematic illustration of an exemplary system comprisinga humidifier positioned on a first stepdeck shipping trailer and adehumidifier positioned on a second stepdeck shipping trailer, accordingto some embodiments;

FIG. 9C shows a schematic illustration of an exemplary system comprisinga humidifier positioned on a first lowboy shipping trailer and adehumidifier positioned on a second lowboy shipping trailer, accordingto some embodiments;

FIG. 10A shows a schematic diagram of an exemplary desalination systemcomprising a combined HDH apparatus and an external heat exchanger,according to some embodiments;

FIG. 10B shows a schematic diagram of an exemplary desalination systemcomprising a combined HDH apparatus, an external heat exchanger, anexternal cooling device, and an external heating device, according tosome embodiments;

FIG. 11 shows a schematic diagram, according to some embodiments, of anexemplary system comprising a pretreatment system, a desalinationsystem, and a precipitation apparatus;

FIG. 12 shows, according to some embodiments, a schematic diagram of anexemplary desalination system comprising a central feed tank, a commonheating fluid source, and two HDH desalination units, each HDHdesalination unit comprising a humidifier, a dehumidifier, a first heatexchanger, and a second heat exchanger; and

FIG. 13 shows, according to some embodiments, a schematic illustrationof an exemplary desalination system comprising an apparatus comprising ahumidification region and a dehumidification region, a precipitationapparatus, a first heat exchanger, a second heating exchanger, and acooling device.

DETAILED DESCRIPTION

Certain embodiments described herein generally relate to apparatusesthat include a vessel comprising a humidification region (e.g., a bubblecolumn humidification region) and a dehumidification region (e.g., abubble column dehumidification region), and associated systems andmethods. In certain embodiments, the apparatuses are configured toinclude various internal features, such as vapor distribution regionsand/or liquid flow control weirs and/or baffles. In some embodiments,mobile humidification-dehumidification (HDH) desalination systems aredescribed that comprise a humidifier (e.g., a bubble column humidifier)having a relatively low height and/or a relatively small footprintand/or a dehumidifier (e.g., a bubble column condenser) having arelatively low height and/or a relatively small footprint. In someembodiments, the mobile HDH desalination system comprises a vesselcomprising a humidification region (e.g., a bubble column humidificationregion) and a dehumidification region (e.g., a bubble columndehumidification region), where the vessel has a relatively low heightand/or a relatively small footprint. In certain cases, the relativelylow height and/or relatively small footprint may facilitate transportand/or installation of the HDH desalination system. In some cases, thesystems described herein allow for simplified, lower cost systems withimproved performance (e.g., higher thermodynamic efficiency). Accordingto some embodiments, the apparatuses may be used in water purificationsystems, such as desalination systems. The water purification systemsmay comprise additional devices external to the apparatuses, such as oneor more heat exchangers, one or more heating devices, and/or one or morecooling devices. Certain embodiments generally relate to methods ofoperating, controlling, and/or cleaning desalination systems comprisinga plurality of desalination units (e.g., HDH desalination units).

While generally embodiments of the invention may employ a variety ofhumidifier and dehumidifier designs, including but not limited to thoseinvolving direct contact between gas and liquid phases, in someembodiments, bubble column humidifiers and bubble column dehumidifiersare described, which may be associated with certain advantages overcertain other types of humidifiers and dehumidifiers. For example,bubble column humidifiers and dehumidifiers may exhibit higherthermodynamic efficiency than certain other types of humidifiers (e.g.,packed bed humidifiers, spray towers, wetted wall towers) anddehumidifiers (e.g., surface condensers). Without wishing to be bound bya particular theory, the increased thermodynamic efficiency may be atleast partially attributed to the use of gas bubbles for heat and masstransfer in bubble column humidifiers and dehumidifiers, since gasbubbles may have more surface area available for heat and mass transferthan other types of surfaces (e.g., metallic tubes, liquid films,packing material). As described in further detail herein, a bubblecolumn humidifier and/or dehumidifier may have certain features thatfurther increase thermodynamic efficiency, including, but not limitedto, relatively low liquid level height, relatively high aspect ratioliquid flow paths, and multi-staged designs. As a result of theirincreased thermodynamic efficiency, bubble column humidifiers and/ordehumidifiers having a certain capacity may be reduced in size comparedto other types of humidifiers and/or dehumidifiers having the samecapacity. In a particular, non-limiting example, a bubble columnhumidifier having a height of 8 feet and a certain diameter may becapable of replacing two packed bed humidifier towers having a combinedheight of 25 feet and the same diameter.

It has been recognized within the context of this invention that it maybe advantageous to combine both a humidification region, for example abubble column humidification region, and a dehumidification region, forexample a bubble column dehumidification region, into a single vessel ofan apparatus. A vessel generally refers to any structure (e.g., a tank)capable of housing a humidification region and a dehumidificationregion. In some cases, a combined humidification-dehumidification (HDH)apparatus (e.g., an apparatus comprising a vessel comprising ahumidification region and a dehumidification region) may have fewercomponents and/or use less material than an HDH system comprising aseparate humidifier (e.g., a bubble column humidifier) and a separatedehumidifier (e.g., a bubble column dehumidifier). For example, an HDHsystem comprising a separate humidifier and dehumidifier may require oneor more ducts (e.g., for gas flow) and/or pipes (e.g., for liquid flow)connecting the humidifier and dehumidifier. In certain cases, the ductsand/or pipes may be expensive and/or burdensome to install. For example,in some industrial facilities (e.g., oil and gas facilities) that arelocated in remote areas, system components may be built off-site asdeployable skids. If a humidifier resides on one skid and a dehumidifierresides on another skid, ducting and/or piping connections may need tobe made during on-site installation, which may lengthen the timerequired for system deployment. In contrast, ducting and/or piping maybe reduced or eliminated in a combined HDH apparatus (e.g., a combinedbubble column apparatus). For example, a combined HDH apparatus mayeliminate the need for ducting between a humidifier gas outlet and adehumidifier gas inlet. In certain embodiments, the combined HDHapparatus comprises one or more gas conduits (e.g., internal gasconduits) in fluid communication with the humidification region and thedehumidification region of the apparatus. In some cases, for example,the one or more gas conduits (e.g., internal gas conduits) are in fluidcommunication with a gas outlet (e.g., a main gas outlet) of thehumidification region and a gas inlet (e.g., a main gas inlet) of thedehumidification region. In some embodiments, the combined HDH apparatusfurther comprises one or more auxiliary gas conduits (e.g., internalauxiliary gas conduits) in fluid communication with an intermediate gasoutlet of the humidification region and an intermediate gas inlet of thedehumidification region. To the extent that ducting is still required,the gas inlets and outlets may be positioned closer together, resultingin less ducting than in HDH systems comprising separate humidifiers anddehumidifiers. This may be advantageous, since ducting used to transportheated, humidified gas in an HDH system may be relatively expensive,large, heavy, and/or rigid. For example, one suitable type of ducting isstainless steel with fiberglass insulation, which is generally capableof accommodating high gas flow rates at high temperatures and/orwithstanding potentially corrosive environments. Installation of suchducting may be challenging due to its relatively large size, heavyweight, and/or high rigidity. Similarly, a combined HDH apparatus mayrequire less piping (e.g., for liquid flow) than an HDH systemcomprising separate humidifiers and dehumidifiers, since liquid inletsand outlets may be positioned in closer proximity to each other. Anyrequired piping may comprise hard pipes, flexible hoses, or any othertype of suitable piping known in the art.

In addition to eliminated or reduced ducting and/or piping, a combinedHDH apparatus (e.g. combined bubble column apparatus) may haveadditional features that allow it to take up less space and/or use fewermaterials than an HDH system comprising a separate humidifier anddehumidifier. For example, a combined HDH apparatus may require lessspace for walkways and/or maintenance points since components may bepositioned closer together. In some cases, a combined HDH apparatus mayalso require less insulating material. For example, an HDH systemcomprising a separate humidifier and dehumidifier may have additionalwalls to be insulated compared to a combined HDH apparatus.

Other aspects of a combined HDH apparatus (e.g. combined bubble columnapparatus) may further reduce cost. For example, the humidification anddehumidification regions of a combined HDH apparatus may have structuralsimilarities, which may advantageously allow certain parts to be used inboth the humidification and dehumidification regions. Due to economiesof scale, a decrease in the number of unique parts in an HDH system mayadvantageously reduce the cost of the HDH system. Reducing the number ofunique parts may also simplify the production process.

According to some embodiments of the invention, an apparatus (e.g., acombined bubble column apparatus) comprises a vessel, and the vesselcomprises a humidification region (e.g., a bubble column humidificationregion) and a dehumidification region (e.g., a bubble columndehumidification region). The humidification region may be configured toreceive a humidification region gas inlet stream from a source of a gasvia at least one humidification region gas inlet. In some cases, the gascomprises at least one non-condensable gas. A non-condensable gasgenerally refers to a gas that cannot be condensed from gas phase toliquid phase under the operating conditions of the apparatus. Examplesof suitable non-condensable gases include, but are not limited to, air,nitrogen, oxygen, helium, argon, carbon monoxide, carbon dioxide, sulfuroxides (SO_(x)) (e.g., SO₂, SO₃), and/or nitrogen oxides (NO_(x)) (e.g.,NO, NO₂). In some embodiments, in addition to the at least onenon-condensable gas, the gas further comprises one or more additionalgases (e.g., the gas may be a gas mixture).

The humidification region may also be configured to receive ahumidification region liquid inlet stream (e.g., liquid feed stream)from a source of a liquid via at least one humidification region liquidinlet. In some embodiments, the liquid comprises a condensable fluid inliquid phase. A condensable fluid generally refers to a fluid that isable to condense from gas phase to liquid phase under the operatingconditions of the apparatus. Non-limiting, illustrative examples ofsuitable condensable fluids include water, ammonia, benzene, toluene,ethyl benzene, and/or alcohols. In addition to the condensable fluid inliquid phase, the liquid may further comprise one or more additionalliquids (e.g., the liquid may be a liquid mixture). In some embodiments,the liquid further comprises one or more contaminants. The one or morecontaminants may, for example, comprise one or more dissolved salts. Adissolved salt generally refers to a salt that has been solubilized tosuch an extent that the component ions (e.g., an anion, a cation) of thesalt are no longer ionically bonded to each other. Non-limiting examplesof dissolved salts that may be present in the liquid include sodiumchloride (NaCl), sodium bromide (NaBr), potassium chloride (KCl),potassium bromide (KBr), ammonium chloride (NH₄Cl), calcium chloride(CaCl₂), magnesium chloride (MgCl₂), sodium carbonate (Na₂CO₃),), sodiumbicarbonate (NaHCO₃), potassium bicarbonate (KHCO₃), sodium sulfate(Na₂SO₄), potassium sulfate (K₂SO₄), calcium sulfate (CaSO₄), magnesiumsulfate (MgSO₄), strontium sulfate (SrSO₄), barium sulfate (BaSO₄),barium-strontium sulfate (BaSr(SO₄)₂), calcium nitrate (Ca(NO₃)₂), iron(III) hydroxide (Fe(OH)₃), iron (III) carbonate (Fe₂(CO₃)₃), aluminumhydroxide (Al(OH)₃), aluminum carbonate (Al₂(CO₃)₃), ammoniumbicarbonate, ammonium sulfate, boron salts, polyacrylic acid sodiumsalts, and/or silicates.

In a particular embodiment, the liquid comprises salt-containing water(e.g., water comprising one or more dissolved salts). In certain cases,the salt-containing water comprises seawater, brackish water, waterproduced form an oil and/or gas extraction process, flowback water,and/or wastewater (e.g., industrial wastewater). Non-limiting examplesof wastewater include textile mill wastewater, leather tannerywastewater, paper mill wastewater, cooling tower blowdown water, fluegas desulfurization wastewater, landfill leachate water, and/or theeffluent of a chemical process (e.g., the effluent of anotherdesalination system and/or chemical process).

In some embodiments, the humidification region liquid inlet stream has arelatively high concentration of one or more contaminants (e.g.,dissolved salts). In certain embodiments, the concentration of one ormore contaminants in the humidification region liquid inlet stream is atleast about 100 mg/L, at least about 200 mg/L, at least about 500 mg/L,at least about 1,000 mg/L, at least about 2,000 mg/L, at least about5,000 mg/L, at least about 10,000 mg/L, at least about 20,000 mg/L, atleast about 50,000 mg/L, at least about 75,000 mg/L, at least about100,000 mg/L, at least about 102,000 mg/L, at least about 110,000 mg/L,at least about 120,000 mg/L, at least about 150,000 mg/L, at least about175,000 mg/L, at least about 200,000 mg/L, at least about 210,000 mg/L,at least about 219,000 mg/L, at least about 220,000 mg/L, at least about250,000 mg/L, at least about 275,000 mg/L, at least about 300,000 mg/L,at least about 310,000 mg/L, at least about 312,000 mg/L, at least about320,000 mg/L, at least about 350,000 mg/L, or at least about 375,000mg/L (and/or, in certain embodiments, up to the solubility limit of theone or more contaminants in the liquid stream). In some embodiments, theconcentration of one or more contaminants in the humidification regionliquid inlet stream is in the range of about 100 mg/L to about 375,000mg/L, about 1,000 mg/L to about 10,000 mg/L, about 1,000 mg/L to about50,000 mg/L, about 1,000 mg/L to about 75,000 mg/L, about 1,000 mg/L toabout 100,000 mg/L, about 1,000 mg/L to about 150,000 mg/L, about 1,000mg/L to about 200,000 mg/L, about 1,000 mg/L to about 250,000 mg/L,about 1,000 mg/L to about 300,000 mg/L, about 1,000 mg/L to about350,000 mg/L, about 1,000 mg/L to about 375,000 mg/L, about 10,000 mg/Lto about 50,000 mg/L, about 10,000 mg/L to about 75,000 mg/L, about10,000 mg/L to about 100,000 mg/L, about 10,000 mg/L to about 150,000mg/L, about 10,000 mg/L to about 200,000 mg/L, about 10,000 mg/L toabout 250,000 mg/L, about 10,000 mg/L to about 300,000 mg/L, about10,000 mg/L to about 350,000 mg/L, about 10,000 mg/L to about 375,000mg/L, about 50,000 mg/L to about 100,000 mg/L, about 50,000 mg/L toabout 150,000 mg/L, about 50,000 mg/L to about 200,000 mg/L, about50,000 mg/L to about 250,000 mg/L, about 50,000 mg/L to about 300,000mg/L, about 50,000 mg/L to about 350,000 mg/L, about 50,000 mg/L toabout 375,000 mg/L, about 100,000 mg/L to about 150,000 mg/L, about100,000 mg/L to about 200,000 mg/L, about 100,000 mg/L to about 250,000mg/L, about 100,000 mg/L to about 300,000 mg/L, about 100,000 mg/L toabout 350,000 mg/L, about 100,000 mg/L to about 375,000 mg/L, about102,000 mg/L to about 219,000 mg/L, about 102,000 mg/L to about 312,000mg/L, about 150,000 mg/L to about 200,000 mg/L, about 150,000 mg/L toabout 250,000 mg/L, about 150,000 mg/L to about 300,000 mg/L, about150,000 mg/L to about 350,000 mg/L, about 150,000 mg/L to about 375,000mg/L, about 200,000 mg/L to about 250,000 mg/L, about 200,000 mg/L toabout 300,000 mg/L, about 200,000 mg/L to about 350,000 mg/L, about200,000 mg/L to about 375,000 mg/L, about 250,000 mg/L to about 300,000mg/L, about 250,000 mg/L to about 350,000 mg/L, about 250,000 mg/L toabout 375,000 mg/L, about 300,000 mg/L to about 350,000 mg/L, or about300,000 mg/L to about 375,000 mg/L. As noted above, the one or morecontaminants may comprise one or more dissolved salts (e.g., NaCl). Theconcentration of a dissolved salt generally refers to the combinedconcentrations of the cation and the anion of the salt. For example, theconcentration of dissolved NaCl would refer to the sum of theconcentration of sodium ions (Na⁺) and the concentration of chlorideions (Cl⁻). The concentration of a contaminant (e.g., a dissolved salt)may be measured according to any method known in the art. For example,methods for measuring the concentration of a contaminant includeinductively coupled plasma (ICP) spectroscopy (e.g., inductively coupledplasma optical emission spectroscopy). As one non-limiting example, anOptima 8300 ICP-OES spectrometer may be used.

In some embodiments, the humidification region liquid inlet streamcontains at least one contaminant (e.g., dissolved salt) in an amount ofat least about 1 wt %, at least about 5 wt %, at least about 10 wt %, atleast about 15 wt %, at least about 20 wt %, at least about 25 wt %, atleast about 26 wt %, at least about 27 wt %, at least about 28 wt %, atleast about 29 wt %, or at least about 30 wt % (and/or, in certainembodiments, up to the solubility limit of the at least one contaminantin the liquid stream). In some embodiments, the humidification regionliquid inlet stream comprises at least one contaminant in an amount inthe range of about 1 wt % to about 10 wt %, about 1 wt % to about 20 wt%, about 1 wt % to about 25 wt %, about 1 wt % to about 26 wt %, about 1wt % to about 27 wt %, about 1 wt % to about 28 wt %, about 1 wt % toabout 29 wt %, about 1 wt % to about 30 wt %, about 10 wt % to about 20wt %, about 10 wt % to about 25 wt %, about 10 wt % to about 26 wt %,about 10 wt % to about 27 wt %, about 10 wt % to about 28 wt %, about 10wt % to about 29 wt %, about 10 wt % to about 30 wt %, about 20 wt % toabout 25 wt %, about 20 wt % to about 26 wt %, about 20 wt % to about 27wt %, about 20 wt % to about 28 wt %, about 20 wt % to about 29 wt %,about 20 wt % to about 30 wt %, about 25 wt % to about 26 wt %, about 25wt % to about 27 wt %, about 25 wt % to about 28 wt %, about 25 wt % toabout 29 wt %, or about 25 wt % to about 30 wt %.

According to some embodiments, the humidification region liquid inletstream has a relatively high total contaminant concentration (e.g.,concentration of all contaminants present in the liquid stream). Incertain cases, the total contaminant concentration of the humidificationregion liquid inlet stream is at least about 1,000 mg/L, at least about2,000 mg/L, at least about 5,000 mg/L, at least about 10,000 mg/L, atleast about 20,000 mg/L, at least about 50,000 mg/L, at least about75,000 mg/L, at least about 100,000 mg/L, at least about 110,000 mg/L,at least about 120,000 mg/L, at least about 150,000 mg/L, at least about175,000 mg/L, at least about 200,000 mg/L, at least about 210,000 mg/L,at least about 220,000 mg/L, at least about 250,000 mg/L, at least about275,000 mg/L, at least about 300,000 mg/L, at least about 310,000 mg/L,at least about 320,000 mg/L, at least about 350,000 mg/L, at least about375,000 mg/L, at least about 400,000 mg/L, at least about 450,000 mg/L,or at least about 500,000 mg/L (and/or, in certain embodiments, up tothe solubility limit of the dissolved contaminant(s) in the liquidstream). In some embodiments, the total contaminant concentration of thehumidification region liquid inlet stream is in the range of about 1,000mg/L to about 10,000 mg/L, about 1,000 mg/L to about 20,000 mg/L, about1,000 mg/L to about 50,000 mg/L, about 1,000 mg/L to about 75,000 mg/L,about 1,000 mg/L to about 100,000 mg/L, about 1,000 mg/L to about150,000 mg/L, about 1,000 mg/L to about 200,000 mg/L, about 1,000 mg/Lto about 250,000 mg/L, about 1,000 mg/L to about 300,000 mg/L, about1,000 mg/L to about 350,000 mg/L, about 1,000 mg/L to about 400,000mg/L, about 1,000 mg/L to about 450,000 mg/L, about 1,000 mg/L to about500,000 mg/L, about 10,000 mg/L to about 20,000 mg/L, about 10,000 mg/Lto about 50,000 mg/L, about 10,000 mg/L to about 75,000 mg/L, about10,000 mg/L to about 100,000 mg/L, about 10,000 mg/L to about 150,000mg/L, about 10,000 mg/L to about 200,000 mg/L, about 10,000 mg/L toabout 250,000 mg/L, about 10,000 mg/L to about 300,000 mg/L, about10,000 mg/L to about 350,000 mg/L, about 10,000 mg/L to about 400,000mg/L, about 10,000 mg/L to about 450,000 mg/L, about 10,000 mg/L toabout 500,000 mg/L, about 20,000 mg/L to about 50,000 mg/L, about 20,000mg/L to about 75,000 mg/L, about 20,000 mg/L to about 100,000 mg/L,about 20,000 mg/L to about 150,000 mg/L, about 20,000 mg/L to about200,000 mg/L, about 20,000 mg/L to about 250,000 mg/L, about 20,000 mg/Lto about 300,000 mg/L, about 20,000 mg/L to about 350,000 mg/L, about20,000 mg/L to about 400,000 mg/L, about 20,000 mg/L to about 450,000mg/L, about 20,000 mg/L to about 500,000 mg/L, about 50,000 mg/L toabout 100,000 mg/L, about 50,000 mg/L to about 150,000 mg/L, about50,000 mg/L to about 200,000 mg/L, about 50,000 mg/L to about 250,000mg/L, about 50,000 mg/L to about 300,000 mg/L, about 50,000 mg/L toabout 350,000 mg/L, about 50,000 mg/L to about 400,000 mg/L, about50,000 mg/L to about 450,000 mg/L, about 50,000 mg/L to about 500,000mg/L, about 100,000 mg/L to about 150,000 mg/L, about 100,000 mg/L toabout 200,000 mg/L, about 100,000 mg/L to about 250,000 mg/L, about100,000 mg/L to about 300,000 mg/L, about 100,000 mg/L to about 350,000mg/L, about 100,000 mg/L to about 400,000 mg/L, about 100,000 mg/L toabout 450,000 mg/L, or about 100,000 mg/L to about 500,000 mg/L.

In some embodiments, the contaminants present in the humidificationregion liquid inlet stream comprise two or more dissolved salts. Theconcentration of a plurality of dissolved salts generally refers to thecombined concentrations of all the cations and anions of the dissolvedsalts. As a simple, non-limiting example, in a liquid stream comprisingdissolved NaCl and dissolved MgSO₄, the total dissolved saltconcentration would refer to the sum of the concentrations of the Na⁺,Cl⁻, Mg²⁺, and SO₄ ²⁻ ions. The total contaminant concentration may bemeasured according to any method known in the art. For example, anon-limiting example of a suitable method for measuring totalcontaminant concentration is the SM 2540C method. According to the SM2540C method, a sample comprising an amount of liquid comprising one ormore dissolved solids is filtered (e.g., through a glass fiber filter),and the filtrate is evaporated to dryness in a weighed dish at 180° C.The increase in dish weight represents the mass of the total dissolvedsolids in the sample. The total contaminant concentration of the samplemay be obtained by dividing the mass of the total dissolved solids bythe volume of the original sample.

In some embodiments, the humidification region liquid inlet stream has atotal contaminant concentration of at least about 1 wt %, at least about5 wt %, at least about 10 wt %, at least about 15 wt %, at least about20 wt %, at least about 25 wt %, at least about 26 wt %, at least about27 wt %, at least about 28 wt %, at least about 29 wt %, or at leastabout 30 wt % (and/or, in certain embodiments, up to the solubilitylimit of the dissolved contaminant(s) in the liquid stream). In someembodiments, the humidification region liquid inlet stream has a totalcontaminant concentration in the range of about 1 wt % to about 10 wt %,about 1 wt % to about 20 wt %, about 1 wt % to about 25 wt %, about 1 wt% to about 26 wt %, about 1 wt % to about 27 wt %, about 1 wt % to about28 wt %, about 1 wt % to about 29 wt %, about 1 wt % to about 30 wt %,about 10 wt % to about 20 wt %, about 10 wt % to about 25 wt %, about 10wt % to about 26 wt %, about 10 wt % to about 27 wt %, about 10 wt % toabout 28 wt %, about 10 wt % to about 29 wt %, about 10 wt % to about 30wt %, about 20 wt % to about 25 wt %, about 20 wt % to about 26 wt %,about 20 wt % to about 27 wt %, about 20 wt % to about 28 wt %, about 20wt % to about 29 wt %, about 20 wt % to about 30 wt %, about 25 wt % toabout 26 wt %, about 25 wt % to about 27 wt %, about 25 wt % to about 28wt %, about 25 wt % to about 29 wt %, or about 25 wt % to about 30 wt %.

In some embodiments, the humidification region is configured to receivethe humidification region liquid inlet stream at a relatively high rate.In some embodiments, the humidification region receives thehumidification region liquid inlet stream at a rate of at least about 40gpm, at least about 50 gpm, at least about 100 gpm, at least about 150gpm, at least about 200 gpm, at least about 300 gpm, at least about 400gpm, at least about 500 gpm, at least about 600 gpm, at least about 700gpm, at least about 800 gpm, at least about 900 gpm, at least about 1000gpm, at least about 1100 gpm, at least about 1200 gpm, at least about1300 gpm, at least about 1400 gpm, at least about 1500 gpm, at leastabout 2000 gpm, at least about 2500 gpm, at least about 3000 gpm, atleast about 3500 gpm, or at least about 4000 gpm. In some embodiments,the humidification region receives the humidification region liquidinlet stream at a rate of about 40 gpm to about 100 gpm, about 40 gpm toabout 150 gpm, about 40 gpm to about 200 gpm, about 40 gpm to about 500gpm, about 40 gpm to about 1000 gpm, about 40 gpm to about 1500 gpm,about 40 gpm to about 2000 gpm, about 40 gpm to about 2500 gpm, about 40gpm to about 3000 gpm, about 40 gpm to about 3500 gpm, about 40 gpm toabout 4000 gpm, about 100 gpm to about 150 gpm, about 100 gpm to about200 gpm, about 100 gpm to about 500 gpm, about 100 gpm to about 1000gpm, about 100 gpm to about 1500 gpm, about 100 gpm to about 2000 gpm,about 100 gpm to about 2500 gpm, about 100 gpm to about 3000 gpm, about100 gpm to about 3500 gpm, about 100 gpm to about 4000 gpm, about 150gpm to about 200 gpm, about 150 gpm to about 500 gpm, about 150 gpm toabout 1000 gpm, about 150 gpm to about 1500 gpm, about 150 gpm to about2000 gpm, about 150 gpm to about 2500 gpm, about 150 gpm to about 3000gpm, about 150 gpm to about 3500 gpm, about 150 gpm to about 4000 gpm,about 200 gpm to about 500 gpm, about 200 gpm to about 1000 gpm, about200 gpm to about 1500 gpm, about 200 gpm to about 2000 gpm, about 200gpm to about 2500 gpm, about 200 gpm to about 3000 gpm, about 200 gpm toabout 3500 gpm, about 200 gpm to about 4000 gpm, about 500 gpm to about1000 gpm, about 500 gpm to about 1500 gpm, about 500 gpm to about 2000gpm, about 500 gpm to about 2500 gpm, about 500 gpm to about 3000 gpm,about 500 gpm to about 3500 gpm, about 500 gpm to about 4000 gpm, about1000 gpm to about 1500 gpm, about 1000 gpm to about 2000 gpm, about 1000gpm to about 2500 gpm, about 1000 gpm to about 3000 gpm, about 1000 gpmto about 3500 gpm, about 1000 gpm to about 4000 gpm, about 1500 gpm toabout 2000 gpm, about 1500 gpm to about 2500 gpm, about 1500 gpm toabout 3000 gpm, about 1500 gpm to about 3500 gpm, about 1500 gpm toabout 4000 gpm, about 2000 gpm to about 3000 gpm, about 2000 gpm toabout 4000 gpm, or about 3000 gpm to about 4000 gpm. In certainembodiments, the humidification region receives the humidificationregion liquid inlet stream at a rate of about 150 gpm to about 1500 gpm.

In the humidification region, the gas may come into contact (e.g.,direct or indirect contact) with the liquid. In some embodiments, thetemperature of the liquid is higher than the temperature of the gas, andupon contact of the gas and the liquid, heat and/or mass may betransferred from the liquid to the gas. According to certainembodiments, at least a portion of the condensable fluid in the liquidis transferred to the gas via an evaporation (e.g., humidification)process, thereby producing a vapor-containing humidification region gasoutlet stream (e.g., an at least partially humidified gas stream) and ahumidification region liquid outlet stream. In some embodiments, thehumidification region gas outlet stream comprises a vapor mixture (e.g.,a mixture of the condensable fluid in vapor phase and thenon-condensable gas). In certain cases, the condensable fluid is water,and the humidification region gas outlet stream is enriched in watervapor relative to the gas received from the humidification region gasinlet. In some embodiments, the humidification region liquid outletstream has a higher concentration of one or more contaminants (e.g.,dissolved salts) than the humidification region liquid inlet stream(e.g., the humidification region liquid outlet stream is enriched in theone or more contaminants relative to the humidification region liquidinlet stream).

According to some embodiments, the humidification region liquid outletstream has a relatively high concentration of one or more contaminants(e.g., dissolved salts). In certain embodiments, the concentration ofone or more contaminants in the humidification region liquid outletstream is at least about 100 mg/L, at least about 200 mg/L, at leastabout 500 mg/L, at least about 1,000 mg/L, at least about 2,000 mg/L, atleast about 5,000 mg/L, at least about 10,000 mg/L, at least about20,000 mg/L, at least about 50,000 mg/L, at least about 75,000 mg/L, atleast about 100,000 mg/L, at least about 150,000 mg/L, at least about200,000 mg/L, at least about 250,000 mg/L, at least about 300,000 mg/L,at least about 350,000 mg/L, at least about 400,000 mg/L, at least about450,000 mg/L, or at least about 500,000 mg/L (and/or, in certainembodiments, up to the solubility limit of the one or more contaminantsin the liquid stream). In some embodiments, the concentration of one ormore contaminants in the humidification region liquid outlet stream isin the range of about 1,000 mg/L to about 10,000 mg/L, about 1,000 mg/Lto about 20,000 mg/L, about 1,000 mg/L to about 50,000 mg/L, about 1,000mg/L to about 100,000 mg/L, about 1,000 mg/L to about 150,000 mg/L,about 1,000 mg/L to about 200,000 mg/L, about 1,000 mg/L to about250,000 mg/L, about 1,000 mg/L to about 300,000 mg/L, about 1,000 mg/Lto about 350,000 mg/L, about 1,000 mg/L to about 400,000 mg/L, about1,000 mg/L to about 450,000 mg/L, about 1,000 mg/L to about 500,000mg/L, about 10,000 mg/L to about 20,000 mg/L, about 10,000 mg/L to about50,000 mg/L, about 10,000 mg/L to about 100,000 mg/L, about 10,000 mg/Lto about 150,000 mg/L, about 10,000 mg/L to about 200,000 mg/L, about10,000 mg/L to about 250,000 mg/L, about 10,000 mg/L to about 300,000mg/L, about 10,000 mg/L to about 350,000 mg/L, about 10,000 mg/L toabout 400,000 mg/L, about 10,000 mg/L to about 450,000 mg/L, about10,000 mg/L to about 500,000 mg/L, about 20,000 mg/L to about 50,000mg/L, about 20,000 mg/L to about 100,000 mg/L, about 20,000 mg/L toabout 150,000 mg/L, about 20,000 mg/L to about 200,000 mg/L, about20,000 mg/L to about 250,000 mg/L, about 20,000 mg/L to about 300,000mg/L, about 20,000 mg/L to about 350,000 mg/L, about 20,000 mg/L toabout 400,000 mg/L, about 20,000 mg/L to about 450,000 mg/L, about20,000 mg/L to about 500,000 mg/L, about 50,000 mg/L to about 100,000mg/L, about 50,000 mg/L to about 150,000 mg/L, about 50,000 mg/L toabout 200,000 mg/L, about 50,000 mg/L to about 250,000 mg/L, about50,000 mg/L to about 300,000 mg/L, about 50,000 mg/L to about 350,000mg/L, about 50,000 mg/L to about 400,000 mg/L, about 50,000 mg/L toabout 450,000 mg/L, about 50,000 mg/L to about 500,000 mg/L, about100,000 mg/L to about 150,000 mg/L, about 100,000 mg/L to about 200,000mg/L, about 100,000 mg/L to about 250,000 mg/L, about 100,000 mg/L toabout 300,000 mg/L, about 100,000 mg/L to about 350,000 mg/L, about100,000 mg/L to about 400,000 mg/L, about 100,000 mg/L to about 450,000mg/L, or about 100,000 mg/L to about 500,000 mg/L.

In some embodiments, the humidification region liquid outlet streamcontains at least one contaminant (e.g., dissolved salt) in an amount ofat least about 1 wt %, at least about 5 wt %, at least about 10 wt %, atleast about 15 wt %, at least about 20 wt %, at least about 25 wt %, atleast about 26 wt %, at least about 27 wt %, at least about 28 wt %, atleast about 29 wt %, or at least about 30 wt % (and/or, in certainembodiments, up to the solubility limit of the contaminant in the liquidstream). In some embodiments, the humidification region liquid outletstream comprises at least one contaminant in an amount in the range ofabout 1 wt % to about 10 wt %, about 1 wt % to about 20 wt %, about 1 wt% to about 25 wt %, about 1 wt % to about 26 wt %, about 1 wt % to about27 wt %, about 1 wt % to about 28 wt %, about 1 wt % to about 29 wt %,about 1 wt % to about 30 wt %, about 10 wt % to about 20 wt %, about 10wt % to about 25 wt %, about 10 wt % to about 26 wt %, about 10 wt % toabout 27 wt %, about 10 wt % to about 28 wt %, about 10 wt % to about 29wt %, about 10 wt % to about 30 wt %, about 20 wt % to about 25 wt %,about 20 wt % to about 26 wt %, about 20 wt % to about 27 wt %, about 20wt % to about 28 wt %, about 20 wt % to about 29 wt %, about 20 wt % toabout 30 wt %, about 25 wt % to about 26 wt %, about 25 wt % to about 27wt %, about 25 wt % to about 28 wt %, about 25 wt % to about 29 wt %, orabout 25 wt % to about 30 wt %.

In some embodiments, the concentration of one or more contaminants inthe humidification region liquid outlet stream is substantially greaterthan the concentration of the one or more contaminants in thehumidification region liquid inlet stream (e.g., liquid feed stream)received by the apparatus. In some cases, the concentration of one ormore contaminants in the humidification region liquid outlet stream isat least about 0.5%, about 1%, about 2%, about 5%, about 10%, about 15%,or about 20% greater than the concentration of the one or morecontaminants in the humidification region liquid inlet stream.

According to some embodiments, the humidification region liquid outletstream has a relatively high total contaminant concentration (e.g.,concentration of all contaminants present in the liquid stream). Incertain cases, the humidification region liquid outlet stream has atotal contaminant concentration of at least about 1,000 mg/L, at leastabout 2,000 mg/L, at least about 5,000 mg/L, at least about 10,000 mg/L,at least about 20,000 mg/L, at least about 50,000 mg/L, at least about75,000 mg/L, at least about 100,000 mg/L, at least about 150,000 mg/L,at least about 200,000 mg/L, at least about 250,000 mg/L, at least about300,000 mg/L, at least about 350,000 mg/L, at least about 400,000 mg/L,at least about 450,000 mg/L, at least about 500,000 mg/L, at least about550,000 mg/L, or at least about 600,000 mg/L (and/or, in certainembodiments, up to the solubility limit of the contaminant(s) in theliquid stream). In some embodiments, the total contaminant concentrationof the humidification region liquid outlet stream is in the range ofabout 10,000 mg/L to about 20,000 mg/L, about 10,000 mg/L to about50,000 mg/L, about 10,000 mg/L to about 100,000 mg/L, about 10,000 mg/Lto about 150,000 mg/L, about 10,000 mg/L to about 200,000 mg/L, about10,000 mg/L to about 250,000 mg/L, about 10,000 mg/L to about 300,000mg/L, about 10,000 mg/L to about 350,000 mg/L, about 10,000 mg/L toabout 400,000 mg/L, about 10,000 mg/L to about 450,000 mg/L, about10,000 mg/L to about 500,000 mg/L, about 10,000 mg/L to about 550,000mg/L, about 10,000 mg/L to about 600,000 mg/L, about 20,000 mg/L toabout 50,000 mg/L, about 20,000 mg/L to about 100,000 mg/L, about 20,000mg/L to about 150,000 mg/L, about 20,000 mg/L to about 200,000 mg/L,about 20,000 mg/L to about 250,000 mg/L, about 20,000 mg/L to about300,000 mg/L, about 20,000 mg/L to about 350,000 mg/L, about 20,000 mg/Lto about 400,000 mg/L, about 20,000 mg/L to about 450,000 mg/L, about20,000 mg/L to about 500,000 mg/L, about 20,000 mg/L to about 550,000mg/L, about 20,000 mg/L to about 600,000 mg/L, about 50,000 mg/L toabout 100,000 mg/L, about 50,000 mg/L to about 150,000 mg/L, about50,000 mg/L to about 200,000 mg/L, about 50,000 mg/L to about 250,000mg/L, about 50,000 mg/L to about 300,000 mg/L, about 50,000 mg/L toabout 350,000 mg/L, about 50,000 mg/L to about 400,000 mg/L, about50,000 mg/L to about 450,000 mg/L, about 50,000 mg/L to about 500,000mg/L, about 50,000 mg/L to about 550,000 mg/L, about 50,000 mg/L toabout 600,000 mg/L, about 100,000 mg/L to about 200,000 mg/L, about100,000 mg/L to about 250,000 mg/L, about 100,000 mg/L to about 300,000mg/L, about 100,000 mg/L to about 350,000 mg/L, about 100,000 mg/L toabout 400,000 mg/L, about 100,000 mg/L to about 450,000 mg/L, about100,000 mg/L to about 500,000 mg/L, about 100,000 mg/L to about 550,000mg/L, or about 100,000 mg/L to about 600,000 mg/L.

In some embodiments, the humidification region liquid outlet stream hasa total contaminant concentration of at least about 10 wt %, at leastabout 15 wt %, at least about 20 wt %, at least about 25 wt %, at leastabout 26 wt %, at least about 27 wt %, at least about 28 wt %, at leastabout 29 wt %, or at least about 30 wt % (and/or, in certainembodiments, up to the solubility limit of the contaminant(s) in theliquid stream). In some embodiments, the humidification region liquidoutlet stream has a total contaminant concentration in the range ofabout 10 wt % to about 20 wt %, about 10 wt % to about 25 wt %, about 10wt % to about 26 wt %, about 10 wt % to about 27 wt %, about 10 wt % toabout 28 wt %, about 10 wt % to about 29 wt %, about 10 wt % to about 30wt %, about 20 wt % to about 25 wt %, about 20 wt % to about 26 wt %,about 20 wt % to about 27 wt %, about 20 wt % to about 28 wt %, about 20wt % to about 29 wt %, about 20 wt % to about 30 wt %, about 25 wt % toabout 26 wt %, about 25 wt % to about 27 wt %, about 25 wt % to about 28wt %, about 25 wt % to about 29 wt %, or about 25 wt % to about 30 wt %.

In some embodiments, the humidification region liquid outlet stream hasa substantially greater total contaminant concentration than thehumidification region liquid inlet stream (e.g., liquid feed stream)received by the apparatus. In some cases, the total contaminantconcentration of the humidification region liquid outlet stream is atleast about 5%, at least about 6%, at least about 10%, at least about14%, at least about 15%, at least about 20%, or at least about 25%greater than the total contaminant concentration of the humidificationregion liquid inlet stream.

In some embodiments, the humidification region is configured to have arelatively high evaporation rate. In certain cases, for example, thehumidification region has an evaporation rate of at least about 50barrels/day, at least about 100 barrels/day, at least about 200barrels/day, at least about 500 barrels/day, at least about 1,000barrels a day, at least about 1,500 barrels/day, at least about 2,000barrels/day, at least about 3,000 barrels/day, at least about 4,000barrels/day, or at least about 5,000 barrels/day. In some embodiments,the humidification region has an evaporation rate of about 50barrels/day to about 500 barrels/day, about 50 barrels/day to about1,000 barrels/day, about 50 barrels/day to about 1,500 barrels/day,about 50 barrels/day to about 2,000 barrels/day, about 50 barrels/day toabout 3,000 barrels/day, about 50 barrels/day to about 4,000barrels/day, about 50 barrels/day to about 5,000 barrels/day, about 100barrels/day to about 500 barrels/day, about 100 barrels/day to about1,000 barrels/day, about 100 barrels/day to about 1,500 barrels/day,about 100 barrels/day to about 2,000 barrels/day, about 100 barrels/dayto about 3,000 barrels/day, about 100 barrels/day to about 4,000barrels/day, about 100 barrels/day to about 5,000 barrels/day, about 200barrels/day to about 1,000 barrels/day, about 200 barrels/day to about1,500 barrels/day, about 200 barrels/day to about 2,000 barrels/day,about 200 barrels/day to about 3,000 barrels/day, about 200 barrels/dayto about 4,000 barrels/day, about 200 barrels/day to about 5,000barrels/day, about 500 barrels/day to about 1,000 barrels/day, about 500barrels/day to about 1,500 barrels/day, about 500 barrels/day to about2,000 barrels/day, about 500 barrels/day to about 3,000 barrels/day,about 500 barrels/day to about 4,000 barrels/day, about 500 barrels/dayto about 5,000 barrels/day, about 1,000 barrels/day to about 2,000barrels/day, about 1,000 barrels/day to about 3,000 barrels/day, about1,000 barrels/day to about 4,000 barrels/day, about 1,000 barrels/day toabout 5,000 barrels/day, about 2,000 barrels/day to about 5,000barrels/day, about 3,000 barrels/day to about 5,000 barrels/day, orabout 4,000 barrels/day to about 5,000 barrels/day. The evaporation rateof the humidification region may be obtained by measuring the totalliquid output volume of the humidification region (e.g., the volume ofthe humidification region liquid output stream and any other liquidoutput streams of the humidification region) over a time period (e.g.,one day) and subtracting the total liquid input volume of thehumidification region (e.g., the volume of the humidification regionliquid inlet stream and any other liquid inlet streams of thehumidification region) over the same time period.

In some embodiments, the humidification region is configured such that aliquid inlet is positioned at a first end (e.g., a top end) of thehumidification region, and a gas inlet is positioned at a second,opposite end (e.g., a bottom end) of the humidification region. Such aconfiguration may facilitate the flow of a liquid stream in a firstdirection (e.g., downwards) through the humidification region and theflow of a gas stream in a second, substantially opposite direction(e.g., upwards) through the humidification region, which mayadvantageously result in high thermal efficiency.

In some embodiments, the dehumidification region of the vessel of thecombined HDH apparatus (e.g., combined bubble column apparatus) isconfigured to receive the humidification region gas outlet stream (e.g.,a heated, at least partially humidified gas stream) via at least onedehumidification region gas inlet as a dehumidification region gas inletstream. The dehumidification region may also be configured to receive adehumidification region liquid inlet stream via at least onedehumidification region liquid inlet. According to some embodiments, thedehumidification region liquid inlet stream comprises the condensablefluid in liquid phase. In some embodiments, for example, thedehumidification region liquid inlet stream comprises water. In certaincases, the dehumidification region liquid inlet stream comprisessubstantially pure water (e.g., water having a relatively low level ofcontaminants).

In the dehumidification region, the dehumidification region gas inletstream (e.g., the heated, at least partially humidified humidificationregion gas outlet stream) may come into contact (e.g., direct orindirect contact) with the dehumidification region liquid inlet stream.The dehumidification region gas inlet stream may have a highertemperature than the dehumidification region liquid inlet stream, andupon contact of the gas and liquid streams, heat and/or mass may betransferred from the dehumidification region gas inlet stream to thedehumidification region liquid inlet stream. In certain embodiments, thedehumidification region gas inlet stream comprises the condensable fluidin vapor phase and the non-condensable gas, and at least a portion ofthe condensable fluid is transferred from the dehumidification regiongas inlet stream to the dehumidification region liquid inlet stream viaa condensation (e.g., dehumidification) process, thereby producing adehumidification region liquid outlet stream comprising the condensablefluid in liquid phase and an at least partially dehumidifieddehumidification region gas outlet stream. In certain cases, thecondensable fluid is water, and the dehumidification region gas outletstream is lean in water vapor relative to the dehumidification regiongas inlet stream (e.g., humidification region gas outlet stream). Insome embodiments, the dehumidification region liquid outlet streamcomprises substantially pure water. In certain cases, thedehumidification region liquid outlet stream comprises water in theamount of at least about 95 wt %, at least about 99 wt %, at least about99.9 wt %, or at least about 99.99 wt % (and/or, in certain embodiments,up to about 99.999 wt %, or more).

According to some embodiments, the dehumidification region liquid outletstream has a relatively low concentration of one or more contaminants(e.g., dissolved salts). In certain embodiments, the concentration ofone or more contaminants in the dehumidification region liquid outletstream is about 500 mg/L or less, about 200 mg/L or less, about 100 mg/Lor less, about 50 mg/L or less, about 20 mg/L or less, about 10 mg/L orless, about 5 mg/L or less, about 2 mg/L or less, about 1 mg/L or less,about 0.5 mg/L or less, about 0.2 mg/L or less, about 0.1 mg/L or less,about 0.05 mg/L or less, about 0.02 mg/L or less, or about 0.01 mg/L orless. In some cases, the concentration of one or more contaminants inthe dehumidification region liquid outlet stream is substantially zero(e.g., not detectable). In certain cases, the concentration of one ormore contaminants in the dehumidification region liquid outlet stream isin the range of about 0 mg/L to about 500 mg/L, about 0 mg/L to about200 mg/L, about 0 mg/L to about 100 mg/L, about 0 mg/L to about 50 mg/L,about 0 mg/L to about 20 mg/L, about 0 mg/L to about 10 mg/L, about 0mg/L to about 5 mg/L, about 0 mg/L to about 2 mg/L, about 0 mg/L toabout 1 mg/L, about 0 mg/L to about 0.5 mg/L, about 0 mg/L to about 0.1mg/L, about 0 mg/L to about 0.05 mg/L, about 0 mg/L to about 0.02 mg/L,or about 0 mg/L to about 0.01 mg/L.

In some embodiments, the dehumidification region liquid outlet streamcontains one or more contaminants in an amount of about 2 wt % or less,about 1 wt % or less, about 0.5 wt % or less, about 0.2 wt % or less,about 0.1 wt % or less, about 0.05 wt % or less, or about 0.01 wt % orless. In some embodiments, the dehumidification region liquid outletstream contains one or more contaminants in an amount in the range ofabout 0.01 wt % to about 2 wt %, about 0.01 wt % to about 1 wt %, about0.01 wt % to about 0.5 wt %, about 0.01 wt % to about 0.2 wt %, or about0.01 wt % to about 0.1 wt %.

In some embodiments, the concentration of one or more contaminants inthe dehumidification region liquid outlet stream is substantially lessthan the concentration of the one or more contaminants in thehumidification region liquid inlet stream (e.g., liquid feed stream)received by the apparatus. In some cases, the concentration of one ormore contaminants in the dehumidification region liquid outlet stream isat least about 0.5%, about 1%, about 2%, about 5%, about 10%, about 15%,or about 20% less than the concentration of the one or more contaminantsin the humidification region liquid inlet stream.

According to some embodiments, the dehumidification region liquid outletstream has a relatively low total contaminant concentration (e.g.,concentration of all contaminants present in the liquid stream). Incertain cases, the dehumidification region liquid outlet stream has atotal contaminant concentration of about 500 mg/L or less, about 200mg/L or less, about 100 mg/L or less, about 50 mg/L or less, about 20mg/L or less, about 10 mg/L or less, about 5 mg/L or less, about 2 mg/Lor less, about 1 mg/L or less, about 0.5 mg/L or less, about 0.2 mg/L orless, about 0.1 mg/L or less, about 0.05 mg/L or less, about 0.02 mg/Lor less, or about 0.01 mg/L or less. In some cases, the totalcontaminant concentration of the dehumidification region liquid outletstream is substantially zero (e.g., not detectable). In certainembodiments, the total contaminant concentration of the dehumidificationregion liquid outlet stream is in the range of about 0 mg/L to about 500mg/L, about 0 mg/L to about 200 mg/L, about 0 mg/L to about 100 mg/L,about 0 mg/L to about 50 mg/L, about 0 mg/L to about 20 mg/L, about 0mg/L to about 10 mg/L, about 0 mg/L to about 5 mg/L, about 0 mg/L toabout 2 mg/L, about 0 mg/L to about 1 mg/L, about 0 mg/L to about 0.5mg/L, about 0 mg/L to about 0.2 mg/L, about 0 mg/L to about 0.1 mg/L,about 0 mg/L to about 0.05 mg/L, about 0 mg/L to about 0.02 mg/L, orabout 0 mg/L to about 0.01 mg/L.

In some embodiments, the dehumidification region liquid outlet streamcontains a total amount of contaminants of about 5 wt % or less, about 2wt % or less, about 1 wt % or less, about 0.5 wt % or less, about 0.2 wt% or less, about 0.1 wt % or less, about 0.05 wt % or less, or about0.01 wt % or less. In some embodiments, the dehumidification regionliquid outlet stream contains a total amount of contaminants in therange of about 0.01 wt % to about 5 wt %, about 0.01 wt % to about 2 wt%, about 0.01 wt % to about 1 wt %, about 0.01 wt % to about 0.5 wt %,about 0.01 wt % to about 0.2 wt %, or about 0.01 wt % to about 0.1 wt %.

In some embodiments, the total contaminant concentration of thedehumidification region liquid outlet stream is substantially less thanthe total contaminant concentration of the humidification region liquidinlet stream (e.g., liquid feed stream) received by the apparatus. Insome cases, the total contaminant concentration of the dehumidificationregion liquid outlet stream is at least about 0.5%, about 1%, about 2%,about 5%, about 10%, about 15%, or about 20% less than the totalcontaminant concentration of the humidification region liquid inletstream.

In some embodiments, the dehumidification region is configured to have arelatively high condensation rate. In certain cases, for example, thedehumidification region has a condensation rate of at least about 50barrels/day, at least about 100 barrels/day, at least about 200barrels/day, at least about 500 barrels/day, at least about 1,000barrels a day, at least about 1,500 barrels/day, at least about 2,000barrels/day, at least about 3,000 barrels/day, at least about 4,000barrels/day, or at least about 5,000 barrels/day. In some embodiments,the dehumidification region has a condensation rate of about 50barrels/day to about 500 barrels/day, about 50 barrels/day to about1,000 barrels/day, about 50 barrels/day to about 1,500 barrels/day,about 50 barrels/day to about 2,000 barrels/day, about 50 barrels/day toabout 3,000 barrels/day, about 50 barrels/day to about 4,000barrels/day, about 50 barrels/day to about 5,000 barrels/day, about 100barrels/day to about 500 barrels/day, about 100 barrels/day to about1,000 barrels/day, about 100 barrels/day to about 1,500 barrels/day,about 100 barrels/day to about 2,000 barrels/day, about 100 barrels/dayto about 3,000 barrels/day, about 100 barrels/day to about 4,000barrels/day, about 100 barrels/day to about 5,000 barrels/day, about 200barrels/day to about 1,000 barrels/day, about 200 barrels/day to about1,500 barrels/day, about 200 barrels/day to about 2,000 barrels/day,about 200 barrels/day to about 3,000 barrels/day, about 200 barrels/dayto about 4,000 barrels/day, about 200 barrels/day to about 5,000barrels/day, about 500 barrels/day to about 1,000 barrels/day, about 500barrels/day to about 1,500 barrels/day, about 500 barrels/day to about2,000 barrels/day, about 500 barrels/day to about 3,000 barrels/day,about 500 barrels/day to about 4,000 barrels/day, about 500 barrels/dayto about 5,000 barrels/day, about 1,000 barrels/day to about 2,000barrels/day, about 1,000 barrels/day to about 3,000 barrels/day, about1,000 barrels/day to about 4,000 barrels/day, about 1,000 barrels/day toabout 5,000 barrels/day, about 2,000 barrels/day to about 5,000barrels/day, about 3,000 barrels/day to about 5,000 barrels/day, orabout 4,000 barrels/day to about 5,000 barrels/day. The condensationrate of the dehumidification region may be obtained by measuring thetotal liquid output volume of the dehumidification region (e.g., thevolume of the dehumidification region liquid output stream and any otherliquid output streams of the dehumidification region) over a time period(e.g., one day) and subtracting the total liquid input volume of thedehumidification region over the same time period.

In some embodiments, the dehumidification region is configured toproduce the dehumidification region liquid outlet stream at a relativelyhigh rate. In some embodiments, the dehumidification region produces thedehumidification region liquid outlet stream at a rate of at least about1,250 barrels/day, at least about 1,500 barrels/day, at least about2,000 barrels/day, at least about 5,000 barrels/day, at least about10,000 barrels/day, at least about 25,000 barrels/day, at least about50,000 barrels/day, at least about 75,000 barrels/day, at least about100,000 barrels/day, or at least about 125,000 barrels/day. In someembodiments, the dehumidification region produces the dehumidificationregion liquid outlet stream at a rate of about 1,250 barrels/day toabout 5,000 barrels/day, about 1,250 barrels/day to about 10,000barrels/day, about 1,250 barrels/day to about 25,000 barrels/day, about1,250 barrels/day to about 50,000 barrels/day, about 1,250 barrels/dayto about 75,000 barrels/day, about 1,250 barrels/day to about 100,000barrels/day, about 1,250 barrels/day to about 125,000 barrels/day, about5,000 barrels/day to about 10,000 barrels/day, about 5,000 barrels/dayto about 25,000 barrels/day, about 5,000 barrels/day to about 50,000barrels/day, about 5,000 barrels/day to about 75,000 barrels/day, about5,000 barrels/day to about 100,000 barrels/day, about 5,000 barrels/dayto about 125,000 barrels/day, about 10,000 barrels/day to about 25,000barrels/day, about 10,000 barrels/day to about 50,000 barrels/day, about10,000 barrels/day to about 75,000 barrels/day, about 10,000 barrels/dayto about 100,000 barrels/day, about 10,000 barrels/day to about 125,000barrels/day, about 50,000 barrels/day to about 100,000 barrels/day, orabout 50,000 barrels/day to about 125,000 barrels/day.

In some embodiments, the dehumidification region is configured such thata liquid inlet is positioned at a first end (e.g., a top end) of thedehumidification region, and a gas inlet is positioned at a second,opposite end (e.g., a bottom end) of the dehumidification region. Such aconfiguration may facilitate the flow of a liquid stream in a firstdirection (e.g., downwards) through the dehumidification region and theflow of a gas stream in a second, substantially opposite direction(e.g., upwards) through the dehumidification region, which mayadvantageously result in high thermal efficiency.

According to some embodiments, the humidification region is a bubblecolumn humidification region. In certain cases, the bubble columnhumidification region comprises at least one stage comprising a chamber.The chamber may, according to some embodiments, comprise a liquid layerand a vapor distribution region (e.g., positioned above the liquidlayer). The vapor distribution region refers to the space within thechamber (e.g., the portion of the chamber not occupied by the liquidlayer) throughout which vapor is distributed. In some cases, the liquidlayer comprises a condensable fluid in liquid phase (e.g., water) andone or more contaminants (e.g., dissolved salts). The chamber may alsobe in fluid communication with a bubble generator, which may act as agas inlet for the at least one stage of the humidification region.

In some embodiments, the dehumidification region is a bubble columndehumidification region. In certain cases, the bubble columndehumidification region comprises at least one stage comprising achamber. The chamber may, according to some embodiments, comprise aliquid layer and a vapor distribution region (e.g., positioned above theliquid layer). In some cases, the liquid layer comprises the condensablefluid in liquid phase. The chamber may also be in fluid communicationwith a bubble generator, which may act as a gas inlet for the at leastone stage of the dehumidification region.

In certain cases, the combined HDH apparatus is a combined bubble columnapparatus that further comprises a gas distribution chamber. In someembodiments, the gas distribution chamber comprises an apparatus gasinlet fluidically connected to a source of a gas (e.g., anon-condensable gas). The gas distribution chamber may comprise a gasdistribution region, which may have sufficient volume to allow the gasto substantially evenly diffuse over the cross section of the combinedbubble column apparatus. The gas distribution region refers to the spacewithin the gas distribution chamber throughout which gas is distributed.In some cases, the gas distribution chamber further comprises a liquidlayer (e.g., a liquid sump volume). For example, liquid (e.g.,comprising the condensable fluid in liquid phase and one or morecontaminants) may collect in the sump volume after exiting thehumidification region. In some cases, the liquid sump volume is indirect contact with a liquid outlet of the combined bubble columnapparatus (e.g., a humidification region liquid outlet). In certainembodiments, the liquid sump volume is in fluid communication with apump that pumps liquid out of the combined bubble column apparatus. Theliquid sump volume may, for example, provide a positive suction pressureon the intake of the pump, and may advantageously prevent negative(e.g., vacuum) suction pressure that could induce deleterious cavitationbubbles. In some cases, the liquid sump volume may advantageouslydecrease the sensitivity of the bubble column apparatus to suddenchanges in heat transfer rates (e.g., due to intermittent feeding ofsalt-containing water to and/or intermittent discharge of pure waterfrom the apparatus). In certain embodiments, such as those embodimentsin which at least the humidification region of the combined bubblecolumn apparatus comprises a plurality of vertically-arranged stages,the gas distribution chamber is positioned at or near the bottom portionof the combined bubble column apparatus (e.g., below the humidificationregion).

In some embodiments, a humidification region gas inlet stream comprisingthe gas (e.g., the non-condensable gas) enters the bubble columnhumidification region. The humidification region gas inlet stream mayflow through the bubble generator of the at least one stage of thehumidification region, thereby forming a plurality of gas bubbles. Insome cases, the gas bubbles flow through the liquid layer of the atleast one stage of the humidification region. As the gas bubblesdirectly contact the liquid layer, which may have a higher temperaturethan the gas bubbles, heat and/or mass (e.g., the condensable fluid) maybe transferred from the liquid layer to the gas bubbles through anevaporation (e.g., humidification) process, thereby forming a heated, atleast partially humidified humidification region gas outlet stream and ahumidification region liquid outlet stream having a higher concentrationof the one or more contaminants than the humidification region liquidinlet stream. In certain embodiments, the condensable fluid is water,and the vapor-containing humidification region gas outlet stream isenriched in water vapor relative to the humidification region gas inletstream received from the humidification region gas inlet. In someembodiments, bubbles of the heated, at least partially humidified gasexit the liquid layer and recombine in the vapor distribution region,and the heated, at least partially humidified gas is substantiallyevenly distributed throughout the vapor distribution region. Thehumidification region gas outlet stream and humidification region liquidoutlet stream may then exit the humidification region.

In some cases, the bubble column dehumidification region is configuredto receive the humidification region gas outlet stream (e.g., comprisingthe heated, at least partially humidified gas) as a dehumidificationregion gas inlet stream. The dehumidification region gas inlet streammay flow through the bubble generator of the at least one stage of thedehumidification region, thereby forming a plurality of bubbles of theheated, at least partially humidified gas. In some cases, the gasbubbles flow through the liquid layer of the at least one stage of thedehumidification region. As the gas bubbles directly contact the liquidlayer, which may have a lower temperature than the gas bubbles, heatand/or mass (e.g., condensable fluid) may be transferred from the gasbubbles to the liquid layer via a condensation (e.g., dehumidification)process, thereby forming a cooled, at least partially dehumidifieddehumidification region gas outlet stream and a dehumidification regionliquid outlet stream comprising the condensable fluid in liquid phase.In certain embodiments, the condensable fluid is water, and thedehumidification region gas outlet stream is lean in water vaporrelative to the dehumidification region gas inlet stream received fromthe dehumidification region gas inlet. In some embodiments, bubbles ofthe cooled, at least partially dehumidified gas exit the liquid layerand recombine in the vapor distribution region, and the cooled, at leastpartially dehumidified gas is substantially evenly distributedthroughout the vapor distribution region. The dehumidification regiongas outlet stream and dehumidification region liquid outlet stream maythen exit the dehumidification region.

FIG. 1A shows, according to some embodiments, a schematiccross-sectional diagram of an exemplary combined bubble column apparatus100 comprising a vessel 150 comprising a bubble column humidificationregion 102 and a bubble column dehumidification region 104. As shown inFIG. 1A, humidification region 102 comprises a single stage comprising ahumidification region liquid inlet 106, a humidification region liquidoutlet 108, and a humidification chamber 110. Liquid layer 112 occupiesa portion of humidification chamber 110. In some embodiments, liquidlayer 112 comprises a condensable fluid in liquid phase (e.g., liquidwater) and one or more contaminants (e.g., dissolved salts). In someembodiments, a vapor distribution region 114 occupies at least a portionof humidification chamber 110 that is not occupied by liquid layer 112.Humidification chamber 110 may, in addition, comprise weir 116, whichmay limit the height of liquid layer 112. Humidification chamber 110 mayalso comprise bubble generator 118, which may be in fluid communicationwith humidification chamber 110 and/or may be arranged withinhumidification chamber 110. In some cases, bubble generator 118 formsthe bottom surface of humidification chamber 110 and/or acts as a gasinlet for humidification chamber 110. In some embodiments, vessel 150 ofapparatus 100 further comprises gas distribution chamber 136 positionedbelow humidification region 102. In FIG. 1A, gas distribution chamber136 is in fluid communication with apparatus gas inlet 138 and withhumidification chamber 110 via bubble generator 118. Bubble generator118 may form a bottom surface of humidification chamber 110 and a topsurface of gas distribution chamber 136. Gas distribution chamber 136may comprise gas distribution region 140, which represents the spacewithin chamber 136 throughout which a gas entering through apparatus gasinlet 138 is distributed.

As shown in FIG. 1A, dehumidification region 104 is positioned abovehumidification region 102. Dehumidification region 104 comprisesdehumidification region liquid inlet 120, dehumidification region liquidoutlet 122, apparatus gas outlet 124, and dehumidification chamber 126.Liquid layer 128 may occupy at least a portion of dehumidificationchamber 126. In some embodiments, liquid layer 128 comprises thecondensable fluid in liquid phase (e.g., liquid water). In someembodiments, a vapor distribution region 130 occupies at least a portionof dehumidification chamber 126 that is not occupied by liquid layer128. In addition, dehumidification chamber 126 may comprise weir 132,which may limit the height of liquid layer 128. In some cases,dehumidification chamber 126 comprises bubble generator 134, which maybe in fluid communication with dehumidification chamber 126 and/or maybe arranged within dehumidification chamber 126. In some cases, bubblegenerator 134 forms the bottom surface of dehumidification chamber 126and/or acts as a gas inlet for dehumidification chamber 126. As shown inFIG. 1A, bubble generator 134 forms a bottom surface of dehumidificationchamber 126 and a top surface of humidification chamber 110.

In operation, a liquid stream comprising the condensable fluid in liquidphase and one or more contaminants may enter humidification region 102through humidification region liquid inlet 106, flowing into liquidlayer 112 in humidification chamber 110. The liquid stream may flowacross humidification chamber 110 to weir 116 and exit humidificationchamber 110 through humidification region liquid outlet 108. Weir 116may maintain the height of liquid layer 112 at the height of weir 116(e.g., excess liquid may flow over weir 116 to humidification regionliquid outlet 108). In dehumidification region 104, a liquid streamcomprising the condensable fluid in liquid phase may enter throughdehumidification region liquid inlet 120, flowing into liquid layer 128in dehumidification chamber 126. The liquid stream may flow acrossdehumidification chamber 126 to weir 132 and exit dehumidificationchamber 126 through dehumidification region liquid outlet 122.

In some cases, apparatus gas inlet 138 is in fluid communication with asource of a gas (e.g., a non-condensable gas). The gas may enter vessel150 of apparatus 100 through apparatus gas inlet 138, flowing into gasdistribution chamber 136. After being substantially homogeneouslydistributed throughout gas distribution region 140 of gas distributionchamber 136, the gas may pass through bubble generator 118, producing aplurality of gas bubbles that travel through liquid layer 112 inhumidification chamber 110. The temperature of liquid layer 112 may behigher than the temperature of the gas bubbles, resulting in transfer ofheat and/or mass from liquid layer 112 to the gas bubbles through ahumidification process. In certain cases, the transfer of heat and/ormass may increase the temperature of the gas, and thus the amount of thecondensable fluid that it can carry. After passing through liquid layer112, the gas, which has been heated and at least partially humidified,may enter vapor distribution region 114 within humidification chamber110. In some cases, the gas may be substantially evenly distributedthroughout vapor distribution region 114. The heated, at least partiallyhumidified gas may then pass through bubble generator 134, therebyforming a plurality of bubbles of the heated, at least partiallyhumidified gas. The bubbles of the heated, at least partially humidifiedgas may then travel through liquid layer 128 in dehumidification chamber126. The liquid (e.g., condensable fluid in liquid phase) of liquidlayer 128 may have a lower temperature than the bubbles of the heated,at least partially humidified gas. As the gas bubbles travel throughliquid layer 128, heat and/or mass may be transferred from the gasbubbles to liquid layer 128 through a dehumidification process. Aftertraveling through liquid layer 128, bubbles of the cooled, at leastpartially dehumidified gas may enter vapor distribution region 130within dehumidification chamber 126. The cooled, at least partiallydehumidified gas may then exit vessel 150 of apparatus 100 via apparatusgas outlet 124.

Appropriate conditions under which to operate the combined HDHapparatuses (e.g., combined bubble column apparatuses) described hereinfor desired performance may be selected by an operator of the systemand/or by an algorithm. In some embodiments, the pressure in the vesselof the combined HDH apparatus may be selected to be approximatelyambient atmospheric pressure during operation. According to certainembodiments, the pressure in the vessel of the combined HDH apparatusmay be selected to be about 90 kPa or less during operation. It may bedesirable, in some embodiments, for the pressure in the humidificationregion of the vessel to be less than approximately ambient atmosphericpressure during operation. In some cases, as the pressure inside thehumidification region decreases, the ability of the humidified carriergas to carry more water vapor increases, allowing for increasedproduction of substantially pure water when the carrier gas isdehumidified in the dehumidification region. Without wishing to be boundby a particular theory, this effect may be explained by the humidityratio, which generally refers to the ratio of water vapor mass to dryair mass in moist air, being higher at pressures lower than atmosphericpressure.

In some embodiments, the combined HDH apparatus (e.g., combined bubblecolumn apparatus) may have a relatively low pressure drop duringoperation. As used herein, the pressure drop across an apparatus refersto the difference between the pressure of a gas stream entering theapparatus at an inlet and the pressure of a gas stream exiting theapparatus at an outlet. In FIG. 1A, for example, the pressure dropacross apparatus 100 would be the difference between the pressure of thegas at apparatus gas inlet 138 and the pressure of the gas at apparatusgas outlet 124. In some cases, the pressure drop may not include theeffect of pressure-increasing devices (e.g., fans, blowers, compressors,pumps). For example, in certain cases, the pressure drop may be obtainedby subtracting the effect of one or more pressure-increasing devices ona gas stream from the difference between the pressure of the gas streamentering the apparatus at an inlet and the pressure of the gas streamexiting the apparatus at an outlet. In some embodiments, the pressuredrop across the apparatus is about 200 kPa or less, about 150 kPa orless, about 100 kPa or less, about 75 kPa or less, about 50 kPa or less,about 20 kPa or less, about 15 kPa or less, about 10 kPa or less, about5 kPa or less, about 2 kPa or less, or about 1 kPa or less. In certainembodiments, the pressure drop across the apparatus (e.g., difference inpressure between the outlet and the inlet) is in the range of about 1kPa to about 2 kPa, about 1 kPa to about 5 kPa, about 1 kPa to about 10kPa, about 1 kPa to about 15 kPa, about 1 kPa to about 20 kPa, about 1kPa to about 50 kPa, about 1 kPa to about 75 kPa, about 1 kPa to about100 kPa, about 1 kPa to about 150 kPa, or about 1 kPa to about 200 kPa.In some embodiments, the pressure of the gas at inlet 138 issubstantially the same as the pressure of the gas at outlet 124 (e.g.,the pressure drop is substantially zero).

In some cases, inlets and/or outlets within the humidification regionand/or the dehumidification region may be provided as separate anddistinct structural elements/features. In some cases, inlets and/oroutlets within the humidification region and/or the dehumidificationregion may be provided by certain components such as the bubblegenerator and/or any other features that establish fluid communicationbetween components of the apparatus. For example, the “gas inlet” and/or“gas outlet” of a humidification region or a dehumidification region maybe provided as a plurality of holes of a bubble generator (e.g., asparger plate). In some embodiments, at least one bubble generator iscoupled to a gas inlet of a stage of the humidification region and/orthe dehumidification region. In some embodiments, a bubble generator iscoupled to a gas inlet of each stage of the humidification region and/ordehumidification region.

The bubble generators may have various features (e.g., holes) used forgeneration of bubbles. The selection of a bubble generator can affectthe size and/or shape of the gas bubbles generated, thereby affectingheat and/or mass transfer between gas bubbles and a liquid layer of ahumidification region or a dehumidification region. Appropriate bubblegenerator and/or bubble generator conditions (e.g., bubble generatorspeeds) may be selected to produce a particular desired set of gasbubbles. Non-limiting examples of suitable bubble generators include asparger plate (e.g., a plate comprising a plurality of holes throughwhich a gas can travel), a device comprising one or more perforatedpipes (e.g., having a radial, annular, spider-web, or hub-and-spokeconfiguration), a device comprising one or more nozzles, and/or porousmedia (e.g., microporous metal).

In some embodiments, a bubble generator comprises a sparger plate. Ithas been recognized that a sparger plate may have certain advantageouscharacteristics. For example, the pressure drop across a sparger platemay be relatively low. Additionally, the simplicity of the sparger platemay render it inexpensive to manufacture and/or resistant to the effectsof fouling. According to some embodiments, the sparger plate comprises aplurality of holes, at least a portion of which have a diameter (ormaximum cross-sectional dimension for non-circular holes) in the rangeof about 0.1 mm to about 50 mm, about 0.1 mm to about 25 mm, about 0.1mm to about 15 mm, about 0.1 mm to about 10 mm, about 0.1 mm to about 5mm, about 0.1 mm to about 1 mm, about 1 mm to about 50 mm, about 1 mm toabout 25 mm, about 1 mm to about 15 mm, about 1 mm to about 10 mm, orabout 1 mm to about 5 mm. In certain embodiments, substantially all theholes of the plurality of holes have a diameter (or maximumcross-sectional dimension) in the range of about 0.1 mm to about 50 mm,about 0.1 mm to about 25 mm, about 0.1 mm to about 15 mm, about 0.1 mmto about 10 mm, about 0.1 mm to about 5 mm, about 0.1 mm to about 1 mm,about 1 mm to about 50 mm, about 1 mm to about 25 mm, about 1 mm toabout 15 mm, about 1 mm to about 10 mm, or about 1 mm to about 5 mm. Theholes may have any suitable shape. For example, at least a portion ofthe plurality of holes may be substantially circular, substantiallyelliptical, substantially square, substantially rectangular,substantially triangular, and/or irregularly shaped. In someembodiments, substantially all the holes of the plurality of holes aresubstantially circular, substantially elliptical, substantially square,substantially rectangular, substantially triangular, and/or irregularlyshaped.

In some cases, the sparger plate may be arranged along the bottomsurface of a stage within the humidification region and/or thedehumidification region. In some embodiments, the sparger plate may havea surface area that covers at least about 50%, at least about 60%, atleast about 70%, at least about 80%, at least about 90%, at least about95%, or about 100% of a cross-section of the humidification regionand/or the dehumidification region.

In some embodiments, a combined HDH apparatus (e.g., a combined bubblecolumn apparatus) further comprises an optional stack. A stack generallyrefers to a structure (e.g., conduit) in fluid communication with a gasoutlet of the combined HDH apparatus, where the maximum cross-sectionaldimension (e.g., diameter) and/or length of the stack is larger than thecorresponding maximum cross-sectional dimension and/or length of the gasoutlet. In some cases, a stack may reduce or eliminate dropletentrainment (e.g., droplets of liquid flowing out of the apparatus withthe gas stream). Without wishing to be bound by a particular theory,increasing the maximum cross-sectional dimension of a conduit throughwhich a gas stream flows will tend to reduce the velocity of the gasstream. As a result, dimensions of the stack may be determined orselected for a given gas stream flow volume that can result in a gasstream velocity in the stack that may be insufficient to entrain anyliquid droplets or at least some liquid droplets that may be present inthe gas stream, the result being that such droplets may fall out of thegas stream instead of exiting the apparatus. For example, in certaincases, the drag force on a liquid droplet (assuming such droplet issubstantially spherical in shape) in a gas stream may be approximated byStokes' Law:

F _(drag)=6πμRV

where F_(drag) is the drag force exerted on the droplet (e.g., by themoving gas stream), μ is the dynamic viscosity of the gas, R is theradius of the droplet, and V is the velocity of the gas relative to thevelocity of the droplet. In some cases, when F_(drag) is greater thanthe gravitational force acting on the droplet, the droplet may remainentrained and may exit the apparatus with the gas stream. In some cases,when F_(drag) is less than the gravitational force acting on thedroplet, the droplet may fall out of the gas stream and return to theapparatus. According to some embodiments, the expanded maximumcross-sectional dimension of the stack (e.g., compared to the maximumcross-sectional dimension of the gas outlet) may cause the velocity ofthe gas stream flowing through the stack (e.g., the dehumidified gasstream) to be reduced. According to Stokes' Law, reducing the velocityof the gas stream flowing through the stack may reduce the drag forceexerted on liquid droplets in the gas stream. In certain cases, the dragforce may be reduced to such an extent that the drag force exerted onthe droplets becomes less than the gravitational force. Accordingly, incertain embodiments, as a gas stream containing entrained liquiddroplets flows into a stack having an expanded cross-sectional dimensionrelative to the gas outlet, one or more of the entrained liquid dropletsmay fall out of the gas stream and return to a liquid layer of theapparatus (e.g., through the gas outlet and/or a separate conduit). In aparticular, non-limiting embodiment, one or more entrained liquiddroplets may fall out of a gas stream flowing through the stack and mayform a surface film on the sides of the stack. In the particularembodiment, liquid droplets may subsequently flow from the surface filmon the sides of the stack to a liquid layer of the apparatus.

FIG. 1B shows, according to some embodiments, a schematic illustrationof an exemplary apparatus 100 comprising optional stack 142 in fluidcommunication with apparatus gas outlet 124. In some cases, stack 142may prevent droplets of liquid from liquid layer 128 from flowing out ofapparatus 100 with a dehumidification region gas outlet stream (e.g., adehumidified gas stream). Instead, liquid droplets present in thedehumidified gas stream may fall out of the dehumidified gas stream andreturn to liquid layer 128 (e.g., through gas outlet 124 and/or aseparate conduit). As shown in FIG. 1B, in some cases, stack 142 has amaximum cross-sectional dimension (e.g., length, diameter) D_(s) that isgreater than the maximum cross-sectional dimension D_(o) of gas outlet124. In certain embodiments, the maximum cross-sectional dimension D_(s)of the stack is at least about 0.01 m, at least about 0.02 m, at leastabout 0.05 m, at least about 0.1 m, at least about 0.2 m, at least about0.5 m, at least about 1 m, at least about 2 m, or at least about 5 mgreater than the maximum cross-sectional dimension D_(o) of the outlet.In some embodiments, maximum cross-sectional dimension D_(s) of thestack is greater than maximum cross-sectional dimension D_(o) of theoutlet by an amount in the range of about 0.01 m to about 0.05 m, about0.01 m to about 0.1 m, about 0.01 m to about 0.5 m, about 0.01 m toabout 1 m, about 0.01 m to about 5 m, about 0.1 m to about 0.5 m, about0.1 m to about 1 m, about 0.1 m to about 5 m, about 0.5 m to about 1 m,about 0.5 m to about 5 m, or about 1 m to about 5 m.

In some embodiments, a combined HDH apparatus (e.g., a combined bubblecolumn apparatus) optionally comprises one or more droplet eliminators.A droplet eliminator generally refers to a device or structureconfigured to prevent entrainment of liquid droplets. Non-limitingexamples of suitable types of droplet eliminators include mesheliminators (e.g., wire mesh mist eliminators), vane eliminators (e.g.,vertical flow chevron vane mist eliminators, horizontal flow chevronvane mist eliminators), cyclonic separators, vortex separators, dropletcoalescers, and/or knockout drums. In some cases, the droplet eliminatormay be configured such that liquid droplets entrained in a gas streamcollide with a portion of the droplet eliminator and fall out of the gasstream. In certain embodiments, the droplet eliminator may extend acrossthe opening (e.g., mouth) of one or more gas outlets.

In some cases, a droplet eliminator may be positioned within a combinedHDH apparatus (e.g., a combined bubble column apparatus) upstream of agas outlet of a humidification region and/or a dehumidification region.For example, in FIG. 1B, combined bubble column apparatus 100 comprisesa first droplet eliminator 144 positioned between humidification chamber110 and dehumidification chamber 126 (e.g., upstream of bubble generator134, which acts as a gas outlet of humidification region 102). Inaddition, combined bubble column apparatus 100 comprises a seconddroplet eliminator 148 positioned between dehumidification chamber 126and apparatus gas outlet 124, which acts as a gas outlet ofdehumidification region 104. In operation, liquid droplets in a gasstream flowing through apparatus 100 may encounter first dropleteliminator 144 and/or second droplet eliminator 148 and return to aliquid layer (e.g., liquid layer 112 and/or liquid layer 128).

In some cases, reducing or eliminating droplet entrainment mayadvantageously increase the amount of condensable fluid in liquid phase(e.g., purified water) recovered from a combined HDH apparatus (e.g., byreducing the amount of condensable fluid lost through an apparatus gasoutlet). In certain embodiments, reducing or eliminating dropletentrainment may increase the amount of condensable fluid in liquid phase(e.g., purified water) recovered from a combined HDH apparatus by atleast about 1%, at least about 5%, at least about 10%, at least about15%, at least about 20%, at least about 30%, at least about 40%, atleast about 50%, or at least about 60%. In some cases, reducing oreliminating droplet entrainment may increase the amount of condensablefluid recovered from a combined HDH apparatus by an amount in the rangeof about 1% to about 10%, about 1% to about 20%, about 1% to about 40%,about 1% to about 60%, about 5% to about 20%, about 5% to about 40%,about 5% to about 60%, about 10% to about 20%, about 10% to about 30%,about 10% to about 40%, about 10% to about 50%, about 10% to about 60%,about 20% to about 30%, about 20% to about 40%, about 20% to about 50%,about 20% to about 60%, about 30% to about 40%, about 30% to about 50%,about 30% to about 60%, about 40% to about 50%, about 40% to about 60%,or about 50% to about 60%.

In some embodiments, a combined HDH apparatus (e.g., a combined bubblecolumn apparatus) optionally comprises a liquid collector. A liquidcollector generally refers to a structure or device configured tocollect a liquid while allowing a gas to freely flow through it.Examples of suitable types of liquid collectors include, but are notlimited to, deck collectors, trough collectors, and vane collectors.According to some embodiments, a liquid collector is configured tocollect water that falls on it from above (e.g., from a dehumidificationregion positioned above the liquid collector) while allowing a gasstream (e.g., a humidification region gas outlet stream comprising aheated, at least partially humidified gas) to freely flow through theliquid collector. In some cases, the liquid collector advantageouslyprevents liquid from a dehumidification region of a combined HDHapparatus from flowing to a humidification region of the combined HDHapparatus. For example, if gas flow through a combined bubble columnapparatus is terminated while liquid remains in one or more stages ofthe dehumidification region, the liquid may exit the one or more stagesthrough one or more bubble generators (e.g., through the holes ofsparger plates). The presence of a liquid collector may, in some cases,prevent the liquid exiting the one or more dehumidification stages fromentering the humidification region. This may avoid, for example, thecommingling of liquid from the dehumidification region, which maycomprise a condensable fluid in liquid phase (e.g., substantially purewater), with liquid from the humidification region, which may comprisethe condensable fluid in liquid phase and one or more contaminants(e.g., salt-containing water). In certain embodiments, the liquidcollector may act as a liquid sump volume for the dehumidificationregion.

In some cases, a liquid collector is positioned between thehumidification region and the dehumidification region of a combined HDHapparatus (e.g., a combined bubble column apparatus). In someembodiments, the liquid collector is positioned between a vapordistribution region of a stage of the humidification region (e.g., thelast stage of the humidification region through which a gas streamflows) and a bubble generator of a stage of the dehumidification region(e.g., the first stage of the dehumidification region through which agas stream flows). In certain embodiments, the liquid collector ispositioned between a droplet eliminator and a bubble generator of astage of the dehumidification region (e.g., the first stage of thedehumidification region through which a gas stream flows). For example,in FIG. 1B, liquid collector 146 is positioned between dropleteliminator 144 and bubble generator 134 of dehumidification chamber 126.

In some embodiments, the humidification region and/or dehumidificationregion of a vessel of a combined HDH apparatus (e.g., a combined bubblecolumn apparatus) comprise a plurality of stages. In some cases, thestages may be arranged such that a gas flows sequentially from a firststage to a second stage. In some cases, the stages may be verticallyarranged (e.g., a second stage may be positioned above or below a firststage in an apparatus) or horizontally arranged (e.g., a second stagemay be positioned to the right or left of a first stage in anapparatus). The stages may be arranged such that a gas stream flowssequentially through a first stage, a second stage, a third stage, andso on. In some cases, each stage may comprise a liquid layer. Inembodiments relating to humidification regions comprising a plurality ofstages (e.g., multi-stage humidification regions), the temperature of aliquid layer of a first stage (e.g., the bottommost stage in avertically arranged humidification region) may be lower than thetemperature of a liquid layer of a second stage (e.g., a stagepositioned above the first stage in a vertically arranged humidificationregion), which may be lower than the temperature of a liquid layer of athird stage (e.g., a stage positioned above the second stage in avertically arranged humidification region). In some embodiments, eachstage in a multi-stage humidification region operates at a temperatureabove that of the previous stage (e.g., the stage below it, inembodiments comprising vertically arranged humidification regions). Inembodiments relating to dehumidification regions comprising a pluralityof stages (e.g., multi-stage dehumidification regions), the temperatureof a liquid layer of a first stage (e.g., the bottommost stage in avertically arranged dehumidification region) may be higher than thetemperature of a liquid layer of a second stage (e.g., a stagepositioned above the first stage in a vertically arrangeddehumidification region), which may be higher than the temperature of aliquid layer of a third stage (e.g., a stage positioned above the secondstage in a vertically arranged dehumidification region). In someembodiments, each stage in a multi-stage dehumidification regionoperates at a temperature below that of the previous stage (e.g., thestage below it, in embodiments comprising vertically arrangeddehumidification regions).

The presence of multiple stages within the humidification region and/ordehumidification region of a combined HDH apparatus may, in some cases,advantageously result in increased humidification and/ordehumidification of a gas. In some cases, the presence of multiplestages may advantageously lead to higher recovery of a condensable fluidin liquid phase. For example, the presence of multiple stages mayprovide numerous locations where the gas may be humidified and/ordehumidified (e.g., treated to recover the condensable fluid). That is,the gas may travel through more than one liquid layer in which at leasta portion of the gas undergoes humidification (e.g., evaporation) ordehumidification (e.g., condensation). In addition, the presence ofmultiple stages may increase the difference in temperature between aliquid stream at an inlet and an outlet of a humidification regionand/or dehumidification region. For example, the use of multiple stagescan produce a dehumidification region liquid outlet stream havingincreased temperature relative to the dehumidification region liquidinlet stream, as discussed more fully below. This may be advantageous insystems where heat from a liquid stream (e.g., dehumidification regionliquid outlet stream) is transferred to a separate stream (e.g.,humidification region liquid inlet stream) within the system. In suchcases, the ability to produce a heated dehumidification region liquidoutlet stream can increase the energy effectiveness of the system.Additionally, the presence of multiple stages may enable greaterflexibility for fluid flow within an apparatus. For example, asdiscussed in further detail below, extraction and/or injection of fluids(e.g., gas streams) from intermediate humidification and/ordehumidification stages may occur through intermediate exchangeconduits.

It should be understood that the humidification region and/ordehumidification region of a vessel of a combined HDH apparatus may haveany number of stages. In some embodiments, the humidification regionand/or dehumidification region may have at least one, at least two, atleast three, at least four, at least five, at least six, at least seven,at least eight, at least nine, or at least ten or more stages. In someembodiments, the humidification region and/or dehumidification regionmay have no more than one, no more than two, no more than three, no morethan four, no more than five, no more than six, no more than seven, nomore than eight, no more than nine, or no more than ten stages. In someembodiments, the stages may be arranged such that they are substantiallyparallel to each other. In certain cases, the stages may be positionedat an angle.

In some cases, at least one stage of the plurality of stages of ahumidification region and/or dehumidification region of a vessel of acombined HDH apparatus comprises a chamber in fluid communication withone or more bubble generators. In some cases, a liquid layer occupies aportion of the chamber. In some embodiments, a vapor distribution regioncomprises at least a portion of the chamber not occupied by the liquidlayer (e.g., the portion of the chamber above the liquid layer). In someembodiments, the vapor distribution region is positioned between twoliquid layers of two consecutive stages. The vapor distribution regionmay, in certain cases, advantageously damp out flow variations createdby random bubbling by allowing a gas to redistribute evenly across thecross section of the vessel of the apparatus. Additionally, in the freespace of the vapor distribution region, large droplets entrained in thegas may have some space to fall back into the liquid layer before thegas enters the subsequent stage. The vapor distribution region may alsoserve to separate two subsequent stages, thereby increasing thethermodynamic effectiveness of the apparatus by keeping the liquidlayers of each stage separate. As discussed in further detail below, thechamber may further comprise one or more weirs and/or baffles to controlliquid flow through the chamber. The chamber may, additionally, compriseone or more conduits (e.g., liquid conduits) to adjacent stages.

FIG. 2A shows a schematic cross-sectional diagram of an exemplarymulti-stage combined bubble column apparatus, according to someembodiments. In FIG. 2A, combined bubble column apparatus 200 comprisesvessel 294 comprising gas distribution chamber 202, humidificationregion 204, and dehumidification region 206. Humidification region 204may be arranged vertically above gas distribution chamber 202, anddehumidification region 206 may be arranged vertically abovehumidification region 204. In some embodiments, gas distribution chamber202 comprises an apparatus gas inlet 208 and a humidification regionliquid outlet 210. Apparatus gas inlet 208 may be fluidically connectedto a source of a first gas comprising a condensable fluid in vapor phaseand/or a non-condensable gas (not shown in FIG. 2A). In some cases, gasdistribution chamber 202 comprises a gas distribution region 212,throughout which a gas entering through apparatus gas inlet 208 issubstantially evenly distributed (e.g., along a bottom surface of bubblegenerator 226). In some embodiments, gas distribution chamber 202further comprises liquid sump volume 214 occupying at least a portion ofgas distribution chamber 202 that is not occupied by gas distributionregion 212. In some cases, liquid collects in sump volume 214 afterexiting humidification region 204 prior to exiting vessel 294 ofapparatus 200. As shown in FIG. 2A, sump volume 214 may be in directcontact with humidification region liquid outlet 210. Sump volume 214and humidification region liquid outlet 210 may, in some cases, be influid communication with a pump that pumps liquid out of vessel 294 ofcombined bubble column apparatus 200 (not shown in FIG. 2A). In somecases, sump volume 214 may provide a positive suction pressure on theintake of the pump and may advantageously prevent negative suctionpressure that may induce cavitation bubbles. Sump volume 214 may alsodecrease the sensitivity of apparatus 200 to sudden changes in heattransfer rates.

As shown in FIG. 2A, humidification region 204 comprises firsthumidification stage 216 and second humidification stage 218, wheresecond humidification stage 218 is arranged vertically above firsthumidification stage 216. First humidification stage 216 compriseschamber 220, which is partially occupied by liquid layer 222. In somecases, liquid layer 222 comprises a condensable fluid in liquid phaseand one or more contaminants (e.g., dissolved salts). A vapordistribution region 224 may occupy at least a portion of humidificationchamber 220 that is not occupied by liquid layer 222 (e.g., the regionabove liquid layer 222). Vapor distribution region 224 may be positionedbetween liquid layer 222 of first humidification stage 216 and liquidlayer 238 of second humidification stage 218. In FIG. 2A, humidificationchamber 220 is in fluid communication with bubble generator 226, whichmay act as a gas inlet of first humidification stage 216 and allow fluidcommunication between gas distribution chamber 202 and firsthumidification stage 216, and bubble generator 244, which may act as agas outlet of first humidification stage 216 and allow fluidcommunication between first humidification stage 216 and secondhumidification stage 218. Bubble generator 226 may occupy substantiallythe entire bottom surface of first humidification stage 216 or mayoccupy a smaller portion of the bottom surface of first humidificationstage 216. Bubble generator 244 may occupy substantially the entire topsurface of first humidification stage 216 or may occupy a smallerportion of the top surface of first humidification stage 216.Humidification chamber 220 may also be in fluid communication withdowncomer 228, which provides a liquid conduit between first stage 216and second stage 218, and downcomer 230, which provides a liquid conduitbetween first stage 216 and gas distribution chamber 202. Downcomer 228,which is positioned between first stage 216 and second stage 218,provides a path for any overflowing condensable fluid (e.g., from liquidlayer 238) to travel from second stage 218 to first stage 216.

Chamber 220 may also comprise one or more liquid flow structures (e.g.,weirs and/or baffles). For example, as shown in FIG. 2A, chamber 220comprises first weir 232 and second weir 234. First weir 232 ispositioned downstream of downcomer 228 and may form a pool surroundingthe outlet of downcomer 228. The outlet of downcomer 228 may besubmerged in the pool, thereby preventing the gas flowing through firststage 216 from flowing to second stage 218 through downcomer 228 insteadof through bubble generator 244. For example, in some cases, the pool ofliquid surrounding the outlet of downcomer 228 has a height higher thanthe height of liquid layer 222 (e.g., the height of weir 232 is higherthan the height of liquid layer 222). This may advantageously result inan increased hydrostatic head around downcomer 228, such that gasbubbles preferentially flow through liquid layer 222 instead of throughthe pool of liquid surrounding downcomer 228 (e.g., the hydrostatic headof liquid that the gas has to overcome is higher in the pool of liquidsurrounding downcomer 228 than in liquid layer 222), preventing the gasfrom bypassing bubble generator 244. In some cases, allowing the gas toflow through downcomer 228 to bypass bubble generator 244 may have thedeleterious effect of disrupting the flow of liquid through apparatus200 and may, in certain cases, stop operation of apparatus 200 entirely.In certain embodiments, the pool of liquid surrounding downcomer 228 hasa height higher than the height of liquid layer 222 and higher than theheight of liquid layer 238. In certain cases, the portion of the bottomsurface of chamber 220 around and/or beneath downcomer 228 (e.g., theportion of the bottom surface of chamber 220 between weir 232 and an endwall) is substantially impermeable to gas flow (e.g., does not comprisea bubble generator), and any pool of liquid surrounding downcomer 228may have a height that is higher than, lower than, or equal to theheight of liquid layer 222 and/or liquid layer 238. In some embodiments,the distance D (e.g., vertical distance) between the top of weir 232 andthe bottom of the outlet of downcomer 228 (indicated as 296 in FIG. 2A)is greater than the height of liquid layer 238. This may, in some cases,advantageously prevent back flow through downcomer 228. In certainembodiments, the distance D (e.g., vertical distance) between the top ofweir 232 and the bottom of the outlet of downcomer 228 is greater thanthe height of liquid layer 222 and greater than the height of liquidlayer 238. In some cases, second weir 234 is positioned upstream ofdowncomer 230 and establishes the maximum height of liquid layer 222,such that any liquid above that height would flow over weir 234, throughdowncomer 230, to liquid sump volume 214. Weir 232 and weir 234 may bepositioned such that liquid entering first humidification stage 216 isdirected to flow from first weir 232 to second weir 234.

Second humidification stage 218 comprises humidification chamber 236 andliquid layer 238 positioned within chamber 236. Liquid layer 238 is influid communication with humidification region liquid inlet 240, whichmay be fluidically connected to a source of a liquid comprising acondensable fluid in liquid phase and one or more contaminants (e.g.,dissolved salts). In some embodiments, a vapor distribution region 242occupies at least a portion of humidification chamber 236 that is notoccupied by liquid layer 238 (e.g., the region above liquid layer 238).In FIG. 2A, humidification chamber 236 is in fluid communication withbubble generator 244, which may act as a gas inlet of secondhumidification stage 218 and allow fluid communication between firsthumidification stage 216 and second humidification stage 218, and bubblegenerator 246, which may act as a gas outlet of second humidificationstage 218 and allow fluid communication between second humidificationstage 218 and first dehumidification stage 250. Bubble generator 244 mayoccupy substantially the entire bottom surface of second humidificationstage 218 or may occupy a smaller portion of the bottom surface ofsecond humidification stage 218. Bubble generator 246 may occupysubstantially the entire top surface of second humidification stage 218or may occupy a smaller portion of the top surface of secondhumidification stage 218. Humidification chamber 236 may also be influid communication with downcomer 228. Humidification chamber 236 mayfurther comprise weir 248, which may be positioned upstream of downcomer228. Weir 248 may establish the maximum height of liquid layer 238, suchthat any liquid that would exceed the height of weir 248 would flow overweir 248, through downcomer 228, and into liquid layer 222 of firsthumidification stage 216. Weir 248 may be positioned such that liquidmay flow across humidification chamber 236 from humidification regionliquid inlet 240 to weir 248.

As shown in FIG. 2A, dehumidification region 206 comprises firstdehumidification stage 250 and second dehumidification stage 252, wheresecond dehumidification stage 252 is arranged vertically above firstdehumidification stage 250. First dehumidification stage 250 comprisesdehumidification chamber 254, which is partially occupied by liquidlayer 256. In some cases, liquid layer 256, which may be in fluidcommunication with dehumidification region liquid outlet 258, comprisesthe condensable fluid in liquid phase (e.g., substantially pure water).A vapor distribution region 260 may occupy at least a portion of chamber254 that is not occupied by liquid layer 256 (e.g., the region aboveliquid layer 256). Vapor distribution region 260 may be positionedbetween liquid layer 256 of first dehumidification stage 250 and liquidlayer 276 of second dehumidification stage 252. In FIG. 2A,dehumidification chamber 254 is in fluid communication with bubblegenerator 246, which may act as a gas inlet of first dehumidificationstage 250 and facilitate fluid communication between secondhumidification stage 218 and first dehumidification stage 250, andbubble generator 262, which may act as a gas outlet of firstdehumidification stage 250 and facilitate fluid communication betweenfirst dehumidification stage 250 and second dehumidification stage 252.Bubble generator 246 may occupy substantially the entire bottom surfaceof first dehumidification stage 250 or may occupy a smaller portion ofthe bottom surface of first dehumidification stage 250. Bubble generator262 may occupy substantially the entire top surface of firstdehumidification stage 250 or may occupy a smaller portion of the topsurface of first dehumidification stage 250.

In FIG. 2A, dehumidification chamber 254 of first dehumidification stage250 is also in fluid communication with downcomer 264, which provides aliquid conduit between first stage 250 and second stage 252 ofdehumidification region 206. Dehumidification chamber 254 may alsocomprise first weir 266 and second weir 268. First weir 266 may belocated downstream of downcomer 264 and may establish a pool of liquidaround the outlet of downcomer 264 having a height higher than theheight of liquid layer 256 (e.g., the height of weir 266 may be higherthan the height of liquid layer 256). First weir 266 may be configuredto prevent a gas stream flowing through first dehumidification stage 250from bypassing bubble generator 262. In some embodiments, the distance(e.g., vertical distance) between the top of first weir 266 and thebottom of the outlet of downcomer 264 is greater than the height ofliquid layer 276. In some embodiments, second weir 268 may be positionedupstream of dehumidification region liquid outlet 258. Second weir 268may establish the maximum height of liquid layer 256 (e.g., any liquidthat would cause the height of liquid layer 256 to exceed the height ofweir 268 would flow over weir 268 and exit through outlet 258). In somecases, dehumidification stage 250 may be configured such that liquidentering first dehumidification stage 250 via downcomer 264 flows fromfirst weir 266 to second weir 268.

Second dehumidification stage 252 comprises dehumidification chamber270, which may be in fluid communication with bubble generator 262,dehumidification region liquid inlet 272, apparatus gas outlet 274, anddowncomer 264. Bubble generator 262 may act as a gas inlet to seconddehumidification stage 252 and may allow fluid communication betweenfirst dehumidification stage 250 and second dehumidification stage 252.For example, bubble generator 262 may be arranged to receive the gasfrom first dehumidification stage 250. Bubble generator 262 may occupysubstantially the entire bottom surface of second stage 252 or mayoccupy a smaller portion of the bottom surface of second stage 252.Downcomer 264 may provide a liquid conduit between first stage 250 andsecond stage 252 of dehumidification region 206. Chamber 270 may be atleast partially occupied by liquid layer 276, which may comprise thecondensable fluid in liquid phase. Liquid layer 276 may be in fluidcommunication with dehumidification region liquid inlet 272. At least aportion of chamber 270 not occupied by liquid layer 276 may comprise avapor distribution region 278, which may be in fluid communication withapparatus gas outlet 274. Dehumidification chamber 270 may also compriseweir 280, which may establish the maximum height of liquid layer 276.Second dehumidification stage 252 may be configured such that liquidflows across chamber 270 from dehumidification region liquid inlet 272to weir 280.

In operation, a first gas stream may enter vessel 294 of apparatus 200via apparatus gas inlet 208, which is in fluid communication with gasdistribution chamber 202. In gas distribution chamber 202, the first gasstream may be substantially homogeneously distributed throughout gasdistribution region 212, along the bottom surface of bubble generator226. The first gas stream may flow through bubble generator 226, therebyforming a plurality of gas bubbles. The gas bubbles may then flowthrough liquid layer 222, which may comprise a condensable fluid inliquid phase (e.g., liquid water) and one or more contaminants (e.g.,dissolved salts). As the gas bubbles flow through liquid layer 222,which may have a higher temperature than the gas bubbles, heat and/ormass (e.g., condensable fluid) may be transferred from liquid layer 222to the gas bubbles through an evaporation (e.g., humidification)process, such that the gas bubbles comprise the condensable fluid invapor phase. In some embodiments, the condensable fluid is water, andthe gas bubbles are at least partially humidified as they travel throughliquid layer 222. Bubbles of the at least partially humidified first gasmay enter vapor distribution region 224 of humidification chamber 220and recombine, resulting in the at least partially humidified first gasstream being substantially evenly distributed throughout vapordistribution region 224.

The at least partially humidified first gas stream may then enterhumidification chamber 236 of second humidification stage 218, flowingthrough bubble generator 244 and forming bubbles of the at leastpartially humidified first gas. The gas bubbles may then flow throughliquid layer 238, which may have a higher temperature than the gasbubbles. As the gas bubbles flow through liquid layer 238, they mayundergo an evaporation process, and heat and/or mass may be transferredfrom liquid layer 238 to the gas bubbles. After exiting liquid layer238, the gas bubbles may enter vapor distribution region 242 ofhumidification chamber 236, where they may recombine and form a furtherheated and humidified first gas stream that is substantiallyhomogeneously distributed throughout vapor distribution region 242,along the bottom surface of bubble generator 246.

The further humidified first gas stream may then enter firstdehumidification stage 250 of dehumidification region 206 through bubblegenerator 246. Bubbles of the further humidified first gas may travelthrough liquid layer 256, which may comprise the condensable fluid inliquid phase (e.g., substantially pure water). The temperature of liquidlayer 256 may be lower than the temperature of the bubbles of thefurther humidified first gas, and heat and/or mass (e.g., condensablefluid) may be transferred from the heated, humidified first gas bubblesto liquid layer 256 through a condensation (e.g., dehumidification)process to form an at least partially dehumidified gas. Bubbles of thecooled, at least partially dehumidified first gas may recombine in vapordistribution region 260 of dehumidification chamber 254. The recombinedcooled, at least partially dehumidified first gas may then enter seconddehumidification stage 252 through bubble generator 262. Bubbles of thecooled, at least partially dehumidified gas may travel through liquidlayer 276, which may have a lower temperature than the gas bubbles. Asthe gas bubbles travel through liquid layer 276, they may be furtherdehumidified, transferring heat and/or mass to liquid layer 276 througha condensation (e.g., dehumidification) process. Bubbles of the furtherdehumidified first gas may recombine in vapor distribution region 278 ofdehumidification chamber 270 and subsequently exit vessel 294 ofcombined bubble column apparatus 200 through apparatus gas outlet 274.

In some embodiments, one or more liquid streams flows through combinedbubble column apparatus 200 (e.g., in substantially the oppositedirection as the first gas stream). According to some embodiments, afirst liquid stream comprising the condensable fluid in liquid phase andone or more contaminants enters vessel 294 of apparatus 200 throughhumidification region liquid inlet 240, which is in fluid communicationwith liquid layer 238 of second humidification stage 218. As the firstliquid stream flows across chamber 236, from humidification regionliquid inlet 240 to weir 248, the first liquid stream (e.g., as part ofliquid layer 238) may directly contact a plurality of gas bubbles havinga temperature lower than the temperature of the first liquid stream.Heat and/or mass may be transferred from the first liquid stream to thegas bubbles through an evaporation (e.g., humidification) process,resulting in a cooled first liquid stream. If the height of liquid layer238 exceeds the height of weir 248, the cooled first liquid stream mayflow over the top of weir 248, through downcomer 228, to a pool ofliquid surrounding the outlet of downcomer 228. If the height of thepool of liquid exceeds the height of weir 232, the cooled first liquidstream may flow over the top of weir 232 to liquid layer 222 of firsthumidification stage 216. As the cooled first liquid stream flows acrosschamber 220 of first humidification stage 216, from weir 232 to weir234, the cooled first liquid stream (e.g., as part of liquid layer 222)may directly contact a plurality of gas bubbles having a temperaturelower than the cooled first liquid stream. Heat and/or mass may betransferred from the cooled first liquid stream to the gas bubblesthrough an evaporation process, resulting in a further cooled firstliquid stream. If the height of liquid layer 222 exceeds the height ofweir 234, the further cooled first liquid stream may flow over the topof weir 234, through downcomer 230, to liquid sump volume 214. Thefurther cooled first liquid stream may then exit vessel 294 of combinedbubble column apparatus 200 through humidification region liquid outlet210.

In some embodiments, a second liquid stream comprising the condensablefluid in liquid phase enters vessel 294 of apparatus 200 throughdehumidification region liquid inlet 272, which is in fluidcommunication with liquid layer 276 of second dehumidification stage252. As the second liquid stream flows across dehumidification chamber270, from dehumidification region liquid inlet 272 to weir 280, thesecond liquid stream (e.g., as part of liquid layer 276) may directlycontact a plurality of gas bubbles having a temperature higher than thetemperature of the second liquid stream. Heat and/or mass may betransferred from the gas bubbles to the second liquid stream, resultingin a heated second liquid stream. If the height of liquid layer 276exceeds the height of weir 280, the heated second liquid stream may flowover the top of weir 280, through downcomer 264, to a pool of liquidsurrounding the outlet of downcomer 264. If the height of the pool ofliquid exceeds the height of weir 266, the heated second liquid streammay flow over the top of weir 266 to liquid layer 256 of firstdehumidification stage 250. As the heated second liquid stream flowsacross chamber 254 of first dehumidification stage 250, from weir 266 toweir 268, the heated second liquid stream (e.g., as part of liquid layer256) may directly contact a plurality of gas bubbles having a highertemperature than the heated second liquid stream. Heat and/or mass maybe transferred from the gas bubbles to the second liquid stream,resulting in a further heated second liquid stream. If the height ofliquid layer 256 exceeds the height of weir 268, the further heatedsecond liquid stream may flow over the top of weir 268 and exit vessel294 of combined bubble column apparatus 200 through dehumidificationregion liquid outlet 258.

In certain embodiments, combined bubble column apparatus 200 furthercomprises one or more additional gas inlets. For example, in FIG. 2B,apparatus 200 further comprises optional second apparatus gas inlet 282.Second apparatus gas inlet 282 may be in fluid communication with asource of a second gas (not shown in FIG. 2B). The composition of thesecond gas may be the same or different as the first gas. In some cases,the second gas may comprise the condensable fluid in vapor phase (e.g.,water vapor) and/or a non-condensable gas. In some embodiments, thefirst and second gases may have different vapor (e.g., water vapor)concentrations. The first and second gases may, in certain cases, havesubstantially the same vapor concentration. In some cases, the first andsecond gases may be maintained at different temperatures. The differencebetween the temperatures of the first and second gases may, in certainembodiments, be at least about 1° C., at least about 5° C., at leastabout 10° C., at least about 20° C., at least about 50° C., at leastabout 100° C., at least about 150° C., or at least about 200° C. Incertain cases, the first and second gases may be maintained atsubstantially the same temperature.

In some embodiments, the one or more additional gas inlets arefluidically connected to one or more additional gas outlets of thecombined bubble column apparatus. As shown in FIG. 2C, combined bubblecolumn apparatus 200 may further comprise optional second apparatus gasoutlet 284. In some cases, second apparatus gas outlet 284 isfluidically connected to second apparatus gas inlet 282 via a gasconduit. In certain cases, second apparatus gas outlet 284 is in fluidcommunication with an intermediate humidification stage (e.g., not thefinal humidification stage). In some embodiments, second apparatus gasinlet 282 is in fluid communication with an intermediatedehumidification stage (e.g., not the first dehumidification stage).

In some cases, extraction from at least one intermediate location in thehumidification region and injection into at least one intermediatelocation in the dehumidification region may be thermodynamicallyadvantageous. Because the portion of a gas flow exiting thehumidification region at an intermediate gas outlet (e.g., the extractedportion) has not passed through the entire humidification region, thetemperature of the gas flow at the intermediate gas outlet (e.g., outlet284) may be lower than the temperature of the gas flow at the main gasoutlet of the humidification region (e.g., bubble generator 246). Thelocations of the intermediate extraction points (e.g., gas outlets)and/or injection points (e.g., gas inlets) may be selected to increasethe thermal efficiency of the system. For example, because a gas (e.g.,air) may have increased vapor content at higher temperatures than atlower temperatures, and because the specific enthalpy of a gas withhigher vapor content may be higher than the specific enthalpy of a gaswith lower vapor content, less gas may be used in higher temperatureareas of the humidification region and/or dehumidification region tobetter balance the heat capacity rate ratios of the gas (e.g., air) andliquid (e.g., water) streams. Extraction and/or injection of a portionof a gas flow at intermediate locations may therefore advantageouslyallow for manipulation of gas mass flows and for greater heat recovery.

However, it should be recognized that in some embodiments, under certainoperating conditions, intermediate extraction and/or injection may notnecessarily or always increase the thermal efficiency of a combined HDHapparatus (e.g., a combined bubble column apparatus). Additionally,there may be certain drawbacks associated with extraction and/orinjection at intermediate locations in some situations. For example,intermediate extraction and/or injection may reduce the condensablefluid (e.g., water) production rate of the apparatus, and there may becertain additional costs associated with intermediate extraction and/orinjection (e.g., costs associated with instrumentation, ducting,insulation, and/or droplet separation). In some cases, if thetemperature difference between a gas flow at an intermediate injectionlocation in the dehumidification region and a gas flow extracted fromthe humidification region and injected in the intermediate injectionlocation is too great, production rates and/or energy efficiency may bedecreased. Accordingly, in some cases, it may be advantageous to buildand/or operate an apparatus without intermediate extraction and/orinjection.

In some embodiments, a combined HDH apparatus (e.g., a combined bubblecolumn apparatus) further comprises additional components that mayenhance apparatus performance. For example, in certain embodiments, thecombined HDH apparatus comprises one or more optional dropleteliminators. As noted above, the presence of one or more dropleteliminators (e.g., extending across the opening of one or more gasoutlets) may advantageously reduce or eliminate droplet entrainment andmay thereby increase the amount of condensable fluid (e.g.,substantially pure water) recovered using the combined HDH apparatus. InFIG. 2D, combined bubble column apparatus 200 comprises a first dropleteliminator 286 positioned upstream of bubble generator 246, which actsas a gas outlet of humidification region 204. As shown in FIG. 2D,combined bubble column apparatus 200 further comprises a second dropleteliminator 290 positioned across the opening of apparatus gas outlet274, which acts as a gas outlet of dehumidification region 206.

According to some embodiments, the combined HDH apparatus (e.g.,combined bubble column apparatus) further comprises an optional liquidcollector. In some cases, the liquid collector is positioned between thehumidification region and the dehumidification region of the vessel ofthe combined HDH apparatus. As noted above, the presence of a liquidcollector may advantageously prevent any liquid (e.g., substantiallypure water) that falls from the dehumidification region from comminglingwith liquid from the humidification region (e.g., salt-containingwater). In FIG. 2D, combined bubble column apparatus 200 comprises aliquid collector 288 positioned between humidification region 204 anddehumidification region 206. In some embodiments, the combined HDHapparatus (e.g., combined bubble column apparatus) comprises an externalliquid sump. In some cases, the presence of an external liquid sump mayadvantageously reduce the weight of the dehumidification region and/orlower the center of mass of the combined HDH apparatus. As shown in FIG.2E, combined bubble column apparatus 200 comprises external liquid sump292, which is in fluid communication with dehumidification region liquidoutlet 258.

While certain embodiments described above have been directed to acombined HDH apparatus (e.g., a combined bubble column apparatus)comprising a dehumidification region arranged vertically above ahumidification region, with each of the humidification anddehumidification regions comprising a plurality of vertically arrangedstages, the combined HDH apparatus may have any suitable structure orarrangement. For example, a humidification region and dehumidificationregion may be arranged vertically (e.g., the dehumidification regionpositioned above or below the humidification region) or horizontally(e.g., the dehumidification region positioned to the right or left ofthe humidification region) within a vessel of a combined HDH apparatus.In some cases, the humidification region and/or dehumidification regionof the combined HDH apparatus comprise a plurality of stages that arevertically arranged or horizontally arranged. In certain embodiments, acombined HDH apparatus comprises a vessel that comprises a verticallyarranged humidification region (e.g., comprising a plurality ofhorizontally or vertically arranged stages) and dehumidification region(e.g., comprising a plurality of horizontally or vertically arrangedstages). In some embodiments, a combined HDH apparatus comprises avessel that comprises a horizontally arranged humidification region(e.g., comprising a plurality of horizontally or vertically arrangedstages) and dehumidification region (e.g., comprising a plurality ofhorizontally or vertically arranged stages).

FIG. 3A shows a schematic illustration of an exemplary combined HDHapparatus (e.g., combined bubble column apparatus) comprising a vesselcomprising a humidification region positioned side-by-side with adehumidification region, according to some embodiments. In FIG. 3A,apparatus 300 comprises vessel 350 comprising humidification region 302and dehumidification region 304 positioned to the left of humidificationregion 302. Humidification region 302 and dehumidification region 304each comprise a plurality of vertically arranged stages. As shown inFIG. 3A, humidification region 302 comprises gas distribution chamber310, first stage 312 positioned above gas distribution chamber 310,second stage 314 positioned above first stage 312, third stage 316positioned above second stage 314, fourth stage 318 positioned abovethird stage 316, fifth stage 320 positioned above fourth stage 318, andsixth stage 322 positioned above fifth stage 320. Gas distributionchamber 310, which may be positioned at the bottom of humidificationregion 302, may be in fluid communication with apparatus gas inlet 306,humidification region liquid outlet 308, and/or first stage 312 (e.g.,through a bubble generator). In some cases, gas distribution chamber 310comprises a gas distribution region and a liquid sump volume. Sixthstage 322, which may be positioned at the top of humidification region302, may be in fluid communication with humidification region liquidinlet 324. In addition, sixth stage 322 may be in fluid communicationwith gas conduit 328 connecting humidification region 302 anddehumidification region 304. In some cases, droplet eliminator 326 maybe positioned between sixth stage 322 and gas conduit 328 to preventliquid droplets from entering gas conduit 328.

Gas conduit 328 may fluidically connect sixth stage 322 ofhumidification region 302 with gas distribution chamber 328 ofdehumidification region 304. Gas conduit 328 may be seen more clearly inFIG. 3B, which shows a schematic illustration of exemplary combined HDHapparatus 300. FIG. 3B additionally illustrates optional auxiliary gasconduit 352, which may fluidically connect an intermediate stage ofhumidification region 302 (e.g., any one of stages 314-320) and anintermediate stage of dehumidification region 304 (e.g., any one ofstages 334-340).

As shown in FIG. 3A, dehumidification region 304 comprises gasdistribution chamber 328, first stage 332 positioned above gasdistribution chamber 328, second stage 334 positioned above first stage332, third stage 336 positioned above second stage 334, fourth stage 338positioned above third stage 336, fifth stage 340 positioned abovefourth stage 338, and sixth stage 342 positioned above fifth stage 340.Gas distribution chamber 328, which may be positioned at the bottom ofdehumidification region 304, may be in fluid communication withdehumidification region liquid outlet 330 and/or first stage 332 (e.g.,through a bubble generator). In some cases, gas distribution chamber 328comprises a gas distribution region and a liquid sump volume. In FIG.3A, sixth stage 342, which is positioned at the top of dehumidificationregion 304, is in fluid communication with dehumidification regionliquid inlet 344 and apparatus gas outlet 348. In some cases, dropleteliminator 346 may be positioned between sixth stage 342 and gas outlet348 to prevent entrainment of liquid droplets from sixth stage 342.

In operation, a gas (e.g., a non-condensable gas) may enter combined HDHapparatus 300 through apparatus gas inlet 306. The gas may travelsequentially through each of stages 312, 314, 316, 318, 320, and 322 ofhumidification region 302. Each stage of humidification region 302 maycomprise a liquid layer comprising a condensable fluid in liquid phaseand one or more contaminants (e.g., dissolved salts). As the gas flowsthrough each stage of humidification region 302 and comes into contactwith each of the liquid layers, the gas may become increasingly heatedand humidified. The heated, humidified gas may then flow through dropleteliminator 326, into gas conduit 328. The heated, humidified gas mayflow through gas conduit 328 to gas distribution chamber 328 ofdehumidification region 304. The heated, humidified gas may subsequentlyflow through each of stages 332, 334, 336, 338, 340, and 342 ofdehumidification region 304. Each stage of dehumidification region 304may comprise a liquid layer comprising the condensable fluid in liquidphase. As the heated, humidified gas flows through each stage ofdehumidification region 304, the heated, humidified gas may becomeincreasingly cooled and dehumidified. The cooled, dehumidified gas maythen exit vessel 350 of combined HDH apparatus 300 through apparatus gasoutlet 348.

In some embodiments, two liquid streams may flow through combined HDHapparatus 300 in directions substantially opposite to the direction ofthe gas stream (e.g., counter-flow to the gas stream). In humidificationregion 302, a first liquid stream comprising a condensable fluid inliquid phase and one or more contaminants (e.g., salt-containing water)may enter sixth stage 322 of humidification region 302 (e.g., theuppermost stage of humidification region 302) through humidificationregion liquid inlet 324. The first liquid stream may then flowsequentially through each of stages 322, 320, 318, 316, 314, and 312 ofhumidification region 302. As the first liquid stream flows through eachstage, the first liquid stream may encounter gas bubbles having atemperature lower than the temperature of the first liquid stream. Heatand/or mass may be transferred from the first liquid stream to the gasbubbles, resulting in a cooled first liquid stream. After flowingthrough each of the stages of humidification region 302, the cooledfirst liquid stream may flow to gas distribution chamber 310 and exitvessel 350 of apparatus 300 through humidification region liquid outlet308.

In dehumidification region 304, a second liquid stream comprising thecondensable fluid in liquid phase (e.g., substantially pure water) mayenter sixth stage 342 of dehumidification region 304 throughdehumidification region liquid inlet 344. The second liquid stream maythen flow sequentially through each of stages 342, 340, 338, 336, 334,and 332 of dehumidification region 304. As the second liquid streamflows through each stage, the second liquid stream may encounter gasbubbles having a higher temperature than the temperature of the secondliquid stream. Heat and/or mass may be transferred from the gas bubblesto the second liquid stream, resulting in a heated second liquid stream.After flowing through each of the stages of dehumidification region 304,the heated second liquid stream may flow to gas distribution chamber 328and exit apparatus 300 through dehumidification region liquid outlet330.

In some embodiments, a combined HDH apparatus (e.g., a combined bubblecolumn apparatus) comprises a horizontally arranged humidificationregion and dehumidification region (e.g., positioned horizontallyadjacent to each other). In certain cases, the horizontally arrangedhumidification and dehumidification regions each comprise a plurality ofhorizontally arranged stages. According to some embodiments, anapparatus comprising a horizontally arranged humidification regioncomprising a plurality of horizontally arranged stages anddehumidification region comprising a plurality of horizontally arrangedstages advantageously has a lower height than an apparatus having otherconfigurations (e.g., a vertically arranged humidification region anddehumidification region, a horizontally arranged humidification anddehumidification region where at least one of the humidification anddehumidification regions comprises a plurality of vertically arrangedstages). In some embodiments, an apparatus comprising a horizontallyarranged humidification region comprising a plurality of horizontallyarranged stages and a dehumidification region comprising a plurality ofhorizontally arranged stages advantageously has a relatively smallfootprint. As used herein, a footprint generally refers to the surfacearea of a bottom surface of an apparatus (e.g., the surface in contactwith the ground).

FIG. 4 shows, according to some embodiments, a schematic cross-sectionalillustration of an exemplary combined bubble column apparatus comprisinga vessel comprising a humidification region positioned side-by-side witha dehumidification region, where both the humidification anddehumidification regions comprise horizontally arranged stages. In FIG.4, combined bubble column apparatus 400 comprises vessel 434 comprisinghumidification region 402 and dehumidification region 404, which ispositioned to the left of humidification region 402. As shown in FIG. 4,humidification region 402 comprises apparatus gas inlet 406,humidification region liquid inlet 408, and humidification region liquidoutlet 410. In addition, humidification region 402 comprises a pluralityof horizontally arranged stages 412A-D. Each of stages 412A-D comprisesa chamber comprising a liquid layer (e.g., one of liquid layers 414A-D)and a vapor distribution region above the liquid layer. Additionally,each of stages 412A-D further comprises a gas conduit (e.g., one of gasconduits 416A-D), and a bubble generator fluidically connected to thegas conduit (e.g., one of bubble generators 418A-D). As shown in FIG. 4,at least a portion of the bubble generator of each stage is positionedbelow a top surface of the liquid layer of the stage, such that a gasflowing through the bubble generator generates gas bubbles that flowthrough the liquid layer of the stage. In a particular, non-limitingexample, bubble generator 418A extends from a top surface of liquidlayer 414A to a bottom surface of stage 412A. In certain embodiments,one or more bubble generators are positioned such that they extendacross a bottom surface of a liquid layer of a stage (e.g., such thatthe gas flows beneath the one or more bubble generators and gas bubblesflow upwards through the liquid layers). FIG. 4 further shows thatstages 412A-D are separated by a plurality of baffles 436A-C. In someembodiments, at least a portion of the baffles comprise a first end incontact with a top surface of a stage of humidification region 402 and asecond end submerged in a liquid layer of the stage. In some cases, oneor more gas conduits traverse one or more baffles. For example, in FIG.4, each of gas conduits 416B-D traverses (e.g., passes through) one ofbaffles 436A-C (e.g., gas conduit 416B traverses baffle 436A, gasconduit 416C traverses baffle 436B, gas conduit 416D traverses baffle436C). The baffles thus may prevent a gas flowing through humidificationregion 402 from bypassing gas conduits 416A-D and bubble generators418A-D. In FIG. 4, baffle 436D, which is traversed by gas conduit 430A,separates humidification region 402 from dehumidification region 404.

In FIG. 4, dehumidification region 404 comprises dehumidification regionliquid inlet 420, dehumidification region liquid outlet 422, andapparatus gas outlet 424. In addition, dehumidification region 404comprises a plurality of horizontally arranged stages 426A-D. Each ofstages 426A-D comprises a chamber comprising a liquid layer (e.g., oneof liquid layers 428A-D) and a vapor distribution region above theliquid layer. Each of stages 426A-D also comprises a gas conduit (e.g.,one of gas conduits 430A-D) and a bubble generator fluidically connectedto the gas conduit (e.g., one of bubble generators 432A-D). As in stages412A-D, in each of stages 426A-D, at least a portion of the bubblegenerator of the stage is positioned below a top surface of the liquidlayer of the stage. In certain embodiments, one or more bubblegenerators are positioned such that they extend across a bottom surfaceof a liquid layer of a stage (e.g., such that the gas flows beneath theone or more bubble generators and gas bubbles flow upwards through theliquid layers). As shown in FIG. 4, stages 426A-D are separated by aplurality of baffles 438A-C. In some embodiments, at least a portion ofthe baffles comprise a first end in contact with a top surface of astage of dehumidification region 404 and a second end submerged in aliquid layer of the stage (e.g., the baffle may extend at least from atop surface of a stage to a top surface of the liquid layer of thestage). In some cases, one or more gas conduits traverse one or morebaffles. For example, in FIG. 4, each of gas conduits 430B-D traversesone of baffles 438A-C (e.g., gas conduit 430B traverses baffle 438A, gasconduit 430C traverses baffle 438B, gas conduit 430D traverses baffle438C). Baffles 438A-C of dehumidification region 404 thus may prevent agas flowing through dehumidification region 404 from bypassing gasconduits 430A-D and bubble generators 432A-D.

In operation, a stream comprising a gas (e.g., a non-condensable gas)may flow through apparatus 400 in a first direction, and one or moreliquid streams may flow through apparatus 400 in a second, substantiallyopposite direction. For example, as shown in FIG. 4, a gas stream mayflow from right to left through apparatus 400, while a first liquidstream comprising a condensable fluid in liquid phase and one or morecontaminants (e.g., salt-containing water) may flow from left to rightthrough humidification region 402 and a second liquid stream comprisingthe condensable fluid in liquid phase (e.g., substantially pure water)may flow from left to right through dehumidification region 404. In FIG.4, the gas stream enters vessel 434 of apparatus 400 through apparatusgas inlet 406. The gas stream may enter first stage 412A ofhumidification region 402, flowing through gas conduit 416A to bubblegenerator 418A and forming a plurality of gas bubbles. The gas bubblesmay subsequently travel through liquid layer 414A, which may have ahigher temperature than the gas bubbles. In liquid layer 414A, heat andmass may be transferred from liquid layer 414A to the gas bubbles toproduce heated, at least partially humidified gas bubbles. Aftertraveling through liquid layer 414A, the gas bubbles may recombine inthe vapor distribution region of first stage 412A positioned aboveliquid layer 414, substantially evenly distributing throughout the vapordistribution region. The heated, at least partially humidified gasstream may then enter second stage 412B, flowing through gas conduit416B to bubble generator 418B. The gas stream may continue to flow fromright to left through humidification region 402, becoming increasinglyheated and humidified as it flows through each stage of humidificationregion 402.

After flowing through each of stages 412A-D of humidification region402, the heated, humidified gas stream may enter first stage 426A ofdehumidification region 404, flowing through gas conduit 430A to bubblegenerator 432A. Bubbles of the heated, humidified gas may be formed andmay travel through liquid layer 428A, which may have a lower temperaturethan the heated, humidified gas bubbles. In liquid layer 428A, heat andmass may be transferred from the heated, humidified gas bubbles toliquid layer 428A. The cooled, at least partially dehumidified gasbubbles may then recombine in the vapor distribution region of firststage 426A, and the cooled, at least partially dehumidified gas streammay flow through gas conduit 430B to bubble generator 432B of secondstage 426B. The cooled, at least partially dehumidified gas stream maycontinue to flow from right to left through dehumidification region 404,becoming increasingly cooled and dehumidified as it flows through eachstage of dehumidification region 404.

While the gas stream flows from right to left through apparatus 400, thefirst liquid stream comprising a condensable fluid in liquid phase andone or more contaminants (e.g., salt-containing water) may flow fromleft to right through humidification region 402. As shown in FIG. 4, thefirst liquid stream may enter humidification region 402 throughhumidification region liquid inlet 408, forming at least a portion ofliquid layer 414D of fourth stage 412D. In fourth stage 412D, heat andmass may be transferred from the first liquid stream in liquid layer414D to bubbles of the gas stream formed by bubble generator 418D, andthe first liquid stream may be cooled. In addition, due to condensablefluid (e.g., water vapor) being transferred from the first liquid streamto the bubbles of the gas stream, the first liquid stream may becomemore concentrated (e.g., the concentration of one or more contaminantsmay increase). As the first liquid stream flows through each of stages412C, 412B, and 412A of humidification region 402, the temperature ofthe first liquid stream may decrease, and the concentration of one ormore contaminants in the stream may increase. The cooled, concentratedliquid stream may then exit vessel 434 of apparatus 400 throughhumidification region liquid outlet 410.

The second liquid stream comprising the condensable fluid in liquidphase (e.g., substantially pure water) may also flow through vessel 434of apparatus 400, flowing from left to right through dehumidificationregion 404. In FIG. 4, the second liquid stream enters dehumidificationregion 404 through dehumidification region water inlet 420, forming atleast a portion of liquid layer 428D of fourth stage 426D. In fourthstage 426D, heat and mass may be transferred from heated, humidified gasbubbles to the second liquid stream. Accordingly, as the second liquidstream flows through each of stages 426D, 426C, 426B, and 426A ofdehumidification region 404, the temperature of the second liquid streammay increase, and the volume of the second liquid stream may alsoincrease. The heated second liquid stream may then exit vessel 434 ofapparatus 400 through dehumidification region liquid outlet 422.

Although certain embodiments of the combined HDH apparatus (e.g.,combined bubble column apparatus) described above comprise ahumidification region positioned to the right of a dehumidificationregion, with a gas stream flowing from right to left and a plurality ofliquid streams flowing from left to right, it should be recognized thatother configurations and other flow directions are also possible. Forexample, in an apparatus comprising a horizontally arrangedhumidification region and dehumidification region, the humidificationregion may be positioned to the right of the dehumidification region. Insome cases, a gas stream may flow from left to right, and one or moreliquid streams may flow from right to left.

According to some embodiments, the combined HDH apparatus (e.g.,combined bubble column apparatus) is substantially continuously operatedand/or configured to facilitate substantially continuous operation. Asused herein, a continuously-operated HDH apparatus (e.g., bubble columnapparatus) refers to an apparatus in which a liquid feed stream is fedto the apparatus at the same rate that a desalinated liquid stream isproduced by the apparatus. In some cases, one or more liquid streams maybe in substantially continuous motion. For example, for bubble columnHDH systems, a liquid feed stream (e.g., a salt-containing water stream)may be fed to the combined bubble column apparatus, substantiallycontinuously flow through one or more stages of the humidificationregion and/or dehumidification region of the apparatus, and result in adesalinated liquid stream (e.g., a substantially pure water stream)subsequently being discharged from the apparatus. In some cases, acontinuously-operated apparatus may be associated with certainadvantages, including, but not limited to, increased uptime and/orenhanced energy performance.

In some embodiments, the combined HDH apparatus (e.g., combined bubblecolumn apparatus) is substantially transiently operated and/orconfigured to facilitate substantially transient operation (e.g., batchprocessing). As used herein, a transiently-operated HDH apparatus refersto an apparatus in which an amount of liquid (e.g., salt-containingwater) is introduced into the apparatus and remains in the apparatusuntil a certain condition (e.g., a certain salinity, a certain density)is reached. Upon satisfaction of the condition, the liquid is dischargedfrom the apparatus. In certain cases, transient operation may allowcleaning operations to be interspersed with production operations. Forexample, transient operation may be advantageous for systems comprisingfilter presses, bioreactors, and/or other systems that may requireperiodic cleaning. In some cases, transient operation may advantageouslyfacilitate processing of highly viscous liquids (e.g., sugar-containingfeedstock) that may be difficult to pump.

FIG. 5 shows a schematic illustration of an exemplary bubble columnapparatus configured for transient operation, according to someembodiments. In FIG. 5, combined bubble column apparatus 500 comprisesvessel 534 comprising humidification region 502 and dehumidificationregion 504. Humidification region 502 comprises humidification chamber510, which is partially occupied by liquid layer 512. In someembodiments, vapor distribution region 514 occupies at least a portionof humidification chamber 510 that is not occupied by liquid layer 512.According to some embodiments, liquid layer 512 comprises a condensablefluid in liquid phase and one or more contaminants (e.g.,salt-containing water). In some cases, liquid layer 512 is in contact(e.g., direct contact) with heating element 506. Heating element 506 maybe any type of device configured to transfer heat to a liquid, such asthe liquid of liquid layer 512. Non-limiting examples of suitableheating elements include an electric heater (e.g., an electric immersionheater), a heat exchanger (e.g., any type of heat exchanger describedherein), and/or a heat pump. In certain embodiments, the heating elementis a heat exchanger fluidically connected to a heat source. Examples ofsuitable heat sources include, but are not limited to, a hot waterboiler (e.g., a gas-fired hot water boiler), waste heat from anindustrial process (e.g., power generation), solar energy, and/or acooling element of one or more dehumidification regions.Dehumidification region 504, which is fluidically connected tohumidification region 502 through bubble generator 524 and to apparatusgas outlet 526, comprises dehumidification chamber 518, which ispartially occupied by liquid layer 520. In some embodiments, vapordistribution region 522 occupies at least a portion of dehumidificationchamber 518 that is not occupied by liquid layer 520. In some cases,liquid layer 520 comprises a condensable fluid in liquid phase (e.g.,substantially pure water). Liquid layer 520 may be in contact (e.g.,direct contact) with cooling element 508. Cooling element 508 may be anytype of device configured to remove heat from a liquid, such as theliquid of liquid layer 520. Non-limiting examples of suitable coolingelements include an electric chiller, a heat exchanger (e.g., any heatexchanger described herein), and/or a heat pump. In certain embodiments,the cooling element is a heat exchanger fluidically connected to a coldsource. Examples of suitable cold sources include, but are not limitedto, air (e.g., for an air-cooled heat exchanger), temperaturestratification in a body of water, and/or a ground-coupled heatexchanger (e.g., with or without a heat pump). As shown in FIG. 5,vessel 534 of apparatus 500 further comprises gas distribution chamber530, which is fluidically connected to apparatus gas inlet 528 and isalso fluidically connected to humidification region 502 through bubblegenerator 516. Gas distribution chamber 530 comprises gas distributionregion 532 (e.g., the space within chamber 530 throughout which a gasmay be distributed). In certain embodiments, apparatus gas outlet 526 isfluidically connected to apparatus gas inlet 528 through a gas conduit(e.g., duct) (not shown in FIG. 5). According to certain embodiments, asingle device may act as both a heating element (e.g., heating element506) of a humidification region and a cooling element (e.g., coolingelement 508) of a dehumidification region. For example, in some cases, aheat pump may act as both a heating element and a cooling element. In aparticular, non-limiting example, both the heating element and thecooling element are heat exchangers. In some cases, an intermediatefluid may transfer heat between the heating element and the coolingelement.

In operation, an amount of liquid comprising the condensable fluid inliquid phase and one or more contaminants (e.g., salt-containing water)may be introduced into humidification region 502 of combined bubblecolumn apparatus 500, forming liquid layer 512. In some cases, an amountof the condensable fluid in liquid phase (e.g., substantially purewater) may also be introduced into dehumidification region 504 ofapparatus 500, forming liquid layer 520.

A gas (e.g., a non-condensable gas) may then enter apparatus 500 throughapparatus gas inlet 528. The gas may flow through gas distributionchamber 530, where the gas may be substantially homogeneouslydistributed throughout gas distribution region 532 of chamber 530, alongthe bottom surface of bubble generator 516. The gas may flow throughbubble generator 516, generating bubbles that travel through liquidlayer 512. As the gas bubbles flow through liquid layer 512, heat andmass may be transferred from liquid layer 512 to the gas bubbles throughan evaporation process, producing heated, humidified gas bubbles.Heating element 506, which is in contact (e.g., direct contact) withliquid layer 512, may replace thermal energy that is lost from liquidlayer 512 in the form of latent and sensible heat. The heated,humidified gas bubbles may recombine in vapor distribution region 514 ofhumidification chamber 510 and flow through bubble generator 524,generating heated, humidified gas bubbles that travel through liquidlayer 520 in dehumidification region 504. As the heated, humidified gasbubbles travel through liquid layer 520 in dehumidification region 504,heat and mass (e.g., condensable fluid in liquid phase) may betransferred from the heated, humidified gas bubbles to liquid layer 520,which has a lower temperature than the gas bubbles, through acondensation process. Cooling element 508, which is in contact (e.g.,direct contact) with liquid layer 520, may remove thermal energy fromliquid layer 520 to prevent or mitigate an increase in the temperatureof liquid layer 520. The bubbles of the at least partially dehumidifiedgas may recombine in vapor distribution region 522 of chamber 518 ofdehumidification region 504 and exit vessel 534 of apparatus 500 throughgas outlet 526.

The gas may continue to flow through vessel 534 of apparatus 500,transferring amounts of condensable fluid from liquid layer 512 ofhumidification region 502 to liquid layer 520 of dehumidification region504, until a certain condition is reached (e.g., the liquid of liquidlayer 512 reaches a certain salinity and/or density, liquid layer 520reaches a certain volume, etc.). In some cases, substantially no liquidis added to or removed from liquid layer 512 and/or 520 (other thanthrough the gas stream) until the condition is satisfied. In certainembodiments, at least a portion of liquid layer 520 is removed fromapparatus 500 prior to satisfaction of the condition (e.g., to preventthe volume of liquid layer 520 from exceeding the volume of chamber518). Upon satisfaction of the condition (e.g., termination of the batchprocess), the liquid of liquid layer 512 and/or the liquid of liquidlayer 520 may be discharged from apparatus 500.

In some embodiments, one or more stages of a humidification regionand/or dehumidification region of a combined HDH apparatus (e.g., acombined bubble column apparatus) have certain advantageouscharacteristics. Some of these characteristics may relate to the liquidlayers of one or more stages of the humidification region and/ordehumidification region. For example, in some cases, one or more stagesmay comprise liquid layers having relatively low heights.

As noted above, one or more stages of a humidification region ordehumidification region may comprise a liquid layer. In some cases, thecomposition of a liquid layer in a stage of the humidification regionmay be different from the composition of a liquid layer in a stage ofthe dehumidification region. For example, in the humidification region,the liquid layer may comprise a liquid comprising a condensable fluid inliquid phase and one or more contaminants (e.g., dissolved salts). Insome embodiments, the liquid layer of the humidification stage comprisessalt-containing water (e.g., brine). In some embodiments, the liquidlayer of the humidification stage comprises seawater, brackish water,water produced form an oil and/or gas extraction process, flowbackwater, and/or wastewater (e.g., industrial wastewater). In thedehumidification region, the liquid layer may comprise the condensablefluid in liquid phase (e.g., water). In certain embodiments, the liquidlayer of the dehumidification stage comprises the condensable fluid inliquid phase in substantially purified form (e.g., having a relativelylow level of contaminants). According to some embodiments, the liquidlayer of the dehumidification stage comprises substantially pure water.

In some embodiments, the height of the liquid layer in one or morestages of the humidification region and/or dehumidification region isrelatively low during operation of the combined HDH apparatus (e.g.,substantially continuous operation and/or substantially transientoperation). In some cases, the height of the liquid layer within a stagecan be measured vertically from the surface of the bubble generator thatcontacts the liquid layer to the top surface of the liquid layer.

Having a relatively low liquid layer height in at least one stage may,in some embodiments, advantageously result in a relatively low pressuredrop between the inlet and outlet of an individual stage. Withoutwishing to be bound by a particular theory, the pressure drop across agiven stage of the humidification region or dehumidification region maybe due, at least in part, to the hydrostatic head of the liquid in thestage that the gas has to overcome. Therefore, the height of the liquidlayer in a stage may be advantageously kept low to reduce the pressuredrop across that stage.

In addition, a relatively low liquid layer height may enhance heatand/or mass transfer. Without wishing to be bound by a particulartheory, in both the humidification region and the dehumidificationregion, the theoretical maximum amount of heat and/or mass transfer mayoccur under conditions where the gas reaches the same temperature as theliquid and the amount of vapor in the gas is exactly at the saturationconcentration. The total area available via the gas-liquid interface atthe bubble surfaces and the residence time of the bubble in the liquid,which is determined by the liquid layer height in each stage (althoughabove a minimum liquid layer height the performance is unaffected), maydetermine how close the heat and/or mass transfer gets to theaforementioned theoretical maximum. Therefore, it may be advantageous tomaintain the liquid layer height at the minimum required to operate thesystem without affecting performance. In some cases, the liquid layerheight is maintained at a height lower than the minimum height to reducethe energy associated with moving air through the system. Althoughhydrostatic head generally varies linearly with respect to liquid layerheight, heat and/or mass transfer efficiency may vary exponentially. Ithas been discovered in the context of this invention that conditions ina bubble column humidification region and/or dehumidification region mayapproach the maximum amount of heat and/or mass transfer at a liquidlayer height of about 1-2 inches.

In some embodiments, during operation of the combined HDH apparatus(e.g., substantially continuous operation and/or substantially transientoperation), the liquid layer within at least one stage of thehumidification region and/or dehumidification region has a height ofabout 0.1 m or less, about 0.09 m or less, about 0.08 m or less, about0.07 m or less, about 0.06 m or less, about 0.05 m or less, about 0.04 mor less, about 0.03 m or less, about 0.02 m or less, about 0.01 m orless, or, in some cases, about 0.005 m or less. In some embodiments,during operation of the combined HDH apparatus, the liquid layer withinat least one stage of the humidification region and/or dehumidificationregion has a height in the range of about 0 m to about 0.1 m, about 0 mto about 0.09 m, about 0 m to about 0.08 m, about 0 m to about 0.07 m,about 0 m to about 0.06 m, about 0 m to about 0.05 m, about 0 m to about0.04 m, about 0 m to about 0.03 m, about 0 m to about 0.02 m, about 0 mto about 0.01 m, about 0 m to about 0.005 m, about 0.005 m to about 0.1m, about 0.005 m to about 0.09 m, about 0.005 m to about 0.08 m, about0.005 m to about 0.07 m, about 0.005 m to about 0.06 m, about 0.005 m toabout 0.05 m, about 0.005 m to about 0.04 m, about 0.005 m to about 0.03m, about 0.005 m to about 0.02 m, or about 0.005 m to about 0.01 m. Insome embodiments, during operation of the combined HDH apparatus (e.g.,substantially continuous operation and/or substantially transientoperation), the liquid layer within each stage of the humidificationregion and/or dehumidification region has a height of about 0.1 m orless, about 0.09 m or less, about 0.08 m or less, about 0.07 m or less,about 0.06 m or less, about 0.05 m or less, about 0.04 m or less, about0.03 m or less, about 0.02 m or less, about 0.01 m or less, or, in somecases, about 0.005 m or less. In some embodiments, during operation ofthe combined HDH apparatus, the liquid layer within each stage of thehumidification region and/or dehumidification region has a height in therange of about 0 m to about 0.1 m, about 0 m to about 0.09 m, about 0 mto about 0.08 m, about 0 m to about 0.07 m, about 0 m to about 0.06 m,about 0 m to about 0.05 m, about 0 m to about 0.04 m, about 0 m to about0.03 m, about 0 m to about 0.02 m, about 0 m to about 0.01 m, about 0 mto about 0.005 m, about 0.005 m to about 0.1 m, about 0.005 m to about0.09 m, about 0.005 m to about 0.08 m, about 0.005 m to about 0.07 m,about 0.005 m to about 0.06 m, about 0.005 m to about 0.05 m, about0.005 m to about 0.04 m, about 0.005 m to about 0.03 m, about 0.005 m toabout 0.02 m, or about 0.005 m to about 0.01 m.

In certain embodiments, the ratio of the height of the liquid layer in astage of the humidification region or dehumidification region to thelength of the stage may be relatively low. The length of the stagegenerally refers to the largest internal cross-sectional dimension ofthe stage. In some embodiments, the ratio of the height of the liquidlayer within at least one stage of the humidification region and/ordehumidification region during operation of the combined HDH apparatus(e.g., substantially continuous operation and/or substantially transientoperation) to the length of the at least one stage is about 1.0 or less,about 0.8 or less, about 0.6 or less, about 0.5 or less, about 0.4 orless, about 0.2 or less, about 0.18 or less, about 0.16 or less, about0.15 or less, about 0.14 or less, about 0.12 or less, about 0.1 or less,about 0.08 or less, about 0.06 or less, about 0.05 or less, about 0.04or less, about 0.02 or less, about 0.01 or less, or, in some cases,about 0.005 or less. In some embodiments, the ratio of the height of theliquid layer within at least one stage of the humidification regionand/or dehumidification region during operation of the combined HDHapparatus to the length of the at least one stage is in the range ofabout 0.005 to about 1.0, about 0.005 to about 0.8, about 0.005 to about0.6, about 0.005 to about 0.5, about 0.005 to about 0.4, about 0.005 toabout 0.2, about 0.005 to about 0.18, about 0.005 to about 0.16, about0.005 to about 0.15, about 0.005 to about 0.14, about 0.005 to about0.12, about 0.005 to about 0.1, about 0.005 to about 0.08, about 0.005to about 0.06, about 0.005 to about 0.05, about 0.005 to about 0.04,about 0.005 to about 0.02, or about 0.005 to about 0.01. In someembodiments, the ratio of the height of the liquid layer within eachstage of the humidification region and/or dehumidification region duringoperation of the combined HDH apparatus (e.g., substantially continuousoperation and/or substantially transient operation) to the length ofeach corresponding stage is about 1.0 or less, about 0.8 or less, about0.6 or less, about 0.5 or less, about 0.4 or less, about 0.2 or less,about 0.18 or less, about 0.16 or less, about 0.15 or less, about 0.14or less, about 0.12 or less, about 0.1 or less, about 0.08 or less,about 0.06 or less, about 0.05 or less, about 0.04 or less, about 0.02or less, about 0.01 or less, or, in some cases, about 0.005 or less. Incertain embodiments, the ratio of the height of the liquid layer withineach stage of the humidification region and/or dehumidification regionduring operation of the combined HDH apparatus to the length of eachcorresponding stage is in the range of about 0.005 to about 1.0, about0.005 to about 0.8, about 0.005 to about 0.6, about 0.005 to about 0.5,about 0.005 to about 0.4, about 0.005 to about 0.2, about 0.005 to about0.18, about 0.005 to about 0.16, about 0.005 to about 0.15, about 0.005to about 0.14, about 0.005 to about 0.12, about 0.005 to about 0.1,about 0.005 to about 0.08, about 0.005 to about 0.06, about 0.005 toabout 0.05, about 0.005 to about 0.04, about 0.005 to about 0.02, orabout 0.005 to about 0.01.

In some embodiments, the height of an individual stage within thehumidification region and/or dehumidification region (e.g., measuredvertically from the bubble generator positioned at the bottom of thestage to the top of the chamber within the stage) may be relatively low.As noted above, reducing the height of one or more stages maypotentially reduce costs and/or potentially increase heat and masstransfer within the system. In some embodiments, the height of at leastone stage of the humidification region and/or dehumidification region isabout 0.5 m or less, about 0.4 m or less, about 0.3 m or less, about 0.2m or less, about 0.1 m or less, or, in some cases, about 0.05 m or less.In certain cases, the height of at least one stage of the humidificationregion and/or dehumidification region is in the range of about 0 m toabout 0.5 m, about 0 m to about 0.4 m, about 0 m to about 0.3 m, about 0m to about 0.2 m, about 0 m to about 0.1 m, about 0 m to about 0.05 m,about 0.05 m to about 0.5 m, about 0.05 m to about 0.4 m, about 0.05 mto about 0.3 m, about 0.05 m to about 0.2 m, or about 0.05 m to about0.1 m. In some embodiments, the height of each stage of thehumidification region and/or dehumidification region is about 0.5 m orless, about 0.4 m or less, about 0.3 m or less, about 0.2 m or less,about 0.1 m or less, or, in some cases, about 0.05 m or less. In certaincases, the height of each stage of the humidification region and/ordehumidification region is in the range of about 0 m to about 0.5 m,about 0 m to about 0.4 m, about 0 m to about 0.3 m, about 0 m to about0.2 m, about 0 m to about 0.1 m, about 0 m to about 0.05 m, about 0.05 mto about 0.5 m, about 0.05 m to about 0.4 m, about 0.05 m to about 0.3m, about 0.05 m to about 0.2 m, or about 0.05 m to about 0.1 m.

In some embodiments, the pressure drop across a stage (i.e. thedifference between inlet gas pressure and outlet gas pressure) for atleast one stage is about 200 kPa or less, about 150 kPa or less, about100 kPa or less, about 75 kPa or less, about 50 kPa or less, about 20kPa or less, about 15 kPa or less, about 10 kPa or less, about 5 kPa orless, or about 1 kPa or less. In certain cases, the pressure drop acrossat least one stage is in the range of about 1 kPa to about 5 kPa, about1 kPa to about 10 kPa, about 1 kPa to about 15 kPa, about 1 kPa to about20 kPa, about 1 kPa to about 50 kPa, about 1 kPa to about 75 kPa, about1 kPa to about 100 kPa, about 1 kPa to about 150 kPa, or about 1 kPa toabout 200 kPa. In some embodiments, the pressure drop across at leastone stage of the humidification region and/or dehumidification region issubstantially zero. In certain cases, the pressure drop across eachstage of the humidification region and/or dehumidification region isabout 200 kPa or less, about 150 kPa or less, about 100 kPa or less,about 75 kPa or less, about 50 kPa or less, about 20 kPa or less, about15 kPa or less, about 10 kPa or less, about 5 kPa or less, or about 1kPa or less. In certain embodiments, the pressure drop across each stageof the humidification region and/or dehumidification region is in therange of about 1 kPa to about 5 kPa, about 1 kPa to about 10 kPa, about1 kPa to about 15 kPa, about 1 kPa to about 20 kPa, about 1 kPa to about50 kPa, about 1 kPa to about 75 kPa, about 1 kPa to about 100 kPa, about1 kPa to about 150 kPa, or about 1 kPa to about 200 kPa. According tocertain embodiments, the pressure drop across each stage of thehumidification region and/or dehumidification region is substantiallyzero.

The stage of a humidification region or dehumidification region of acombined HDH apparatus (e.g., a combined bubble column apparatus) mayhave any shape suitable for a particular application. In someembodiments, at least one stage of a humidification region and/ordehumidification region has a cross-sectional shape that issubstantially circular, substantially elliptical, substantially square,substantially rectangular, substantially triangular, or irregularlyshaped. In some embodiments, at least one stage of a humidificationregion and/or dehumidification region has a relatively large aspectratio. As used herein, the aspect ratio of a stage refers to the ratioof the length of the stage to the width of the stage. The length of thestage may refer to the largest internal cross-sectional dimension of thestage (e.g., in a plane perpendicular to a vertical axis of the stage),and the width of the stage may refer to the largest cross-sectionaldimension of the stage (e.g., in a plane perpendicular to a verticalaxis of the stage) measured perpendicular to the length.

In some embodiments, at least one stage of a humidification regionand/or dehumidification region of a combined HDH apparatus (e.g., acombined bubble column apparatus) has an aspect ratio of at least about1.5, at least about 2, at least about 5, at least about 10, at leastabout 15, or at least about 20. In some embodiments, at least one stageof a humidification region and/or dehumidification region has an aspectratio in the range of about 1.5 to about 5, about 1.5 to about 10, about1.5 to about 15, about 1.5 to about 20, about 2 to about 5, about 2 toabout 10, about 2 to about 15, about 2 to about 20, about 5 to about 10,about 5 to about 15, about 5 to about 20, about 10 to about 15, about 10to about 20, or about 15 to about 20. In some embodiments, each stage ofa humidification region and/or dehumidification region of a combined HDHapparatus has an aspect ratio of at least about 1.5, at least about 2,at least about 5, at least about 10, at least about 15, or at leastabout 20. In some embodiments, each stage of a humidification regionand/or dehumidification region of a combined HDH apparatus has an aspectratio in the range of about 1.5 to about 5, about 1.5 to about 10, about1.5 to about 15, about 1.5 to about 20, about 2 to about 5, about 2 toabout 10, about 2 to about 15, about 2 to about 20, about 5 to about 10,about 5 to about 15, about 5 to about 20, about 10 to about 15, about 10to about 20, or about 15 to about 20.

In some embodiments, one or more weirs in one or more stages of ahumidification region and/or dehumidification region of a combined HDHapparatus (e.g., a combined bubble column apparatus) are positionedwithin a chamber of the stage so as to control or direct flow of aliquid (e.g., within one stage and/or between two or more stages).

In some embodiments, the maximum height of a liquid layer in one or morestages of a humidification region and/or dehumidification region may beset by one or more weirs. As used herein, a weir refers to a structurethat obstructs liquid flow in a stage. In some cases, a weir may bepositioned adjacent or surrounding a region of the chamber where liquidmay flow out of the chamber, for example, into a different chamberbelow. For example, if a weir is positioned upstream of a liquid outlet,any additional liquid that would cause the height of a liquid layer toexceed the height of the weir would flow over the weir and exit thestage through the liquid outlet.

In some embodiments, one or more weirs create a pool of liquidsurrounding an outlet of a liquid conduit between two stages. In someembodiments, a weir is positioned adjacent or surrounding a region ofthe stage that receives a stream of liquid from, for example, adifferent chamber above the region or adjacent to the region. Forexample, a first stage may be positioned vertically below a secondstage, and the liquid outlet of the second stage may be a downcomer thatfeeds into the first stage. A weir may be positioned immediatelydownstream of the downcomer, such that the weir either encircles thedowncomer or extends all the way to the walls of the chamber to create apool in which the outlet of the downcomer is submerged. The pool mayprevent air from entering the downcomer. In some cases, the height ofthe pool is greater than the height of the liquid layer in the firststage (e.g., the height of the weir is greater than the height of theliquid layer in the first stage). Otherwise, the hydrostatic head forair sparging through the liquid layer in the first stage would begreater than the hydrostatic head required for air to flow up thedowncomer. Accordingly, a pool height greater than the height of theliquid layer in the first stage may advantageously prevent air fromflowing up the downcomer. In some embodiments, as additional liquid isintroduced into the pool and the height of the liquid in the poolexceeds the height of the weir, excess liquid may flow over the top ofthe weir (e.g., into the liquid layer of the first stage). In certainembodiments, the distance (e.g., vertical distance) between the top of aweir creating a pool encircling a downcomer and the bottom of an outletof the downcomer is greater than the height of the liquid layer in thesecond stage. In some cases, this may advantageously prevent back flowthrough the downcomer.

In some cases, a weir may be positioned within a chamber so as to notcontact one or more walls of the chamber. In some cases, a weir may bepositioned within a chamber so as to contact one or more walls of thechamber.

The one or more weirs may be selected to have a height that is less thanthe height of the chamber. In some embodiments, the height of the weirsmay determine the maximum height for a liquid layer in the chamber. Forexample, if a liquid layer residing in a first chamber reaches a heightthat exceeds the height of a weir positioned along a bottom surface ofthe chamber, then at least a portion of the excess liquid may flow overthe weir. In some cases, the excess liquid may flow into a second,adjacent chamber, e.g., a chamber positioned below the first chamber. Insome embodiments, at least one weir in a chamber has a height of about0.1 m or less, about 0.09 m or less, about 0.08 m or less, about 0.07 mor less, about 0.06 m or less, about 0.05 m or less, about 0.04 m orless, about 0.03 m or less, about 0.02 m or less, about 0.01 m or less,or, in some cases, about 0.005 m or less. In some embodiments, at leastone weir in a chamber has a height in the range of about 0 m to about0.1 m, about 0 m to about 0.09 m, about 0 m to about 0.08 m, about 0 mto about 0.07 m, about 0 m to about 0.06 m, about 0 m to about 0.05 m,about 0 m to about 0.04 m, about 0 m to about 0.03 m, about 0 m to about0.02 m, about 0 m to about 0.01 m, about 0 m to about 0.005 m, about0.005 m to about 0.1 m, about 0.005 m to about 0.09 m, about 0.005 m toabout 0.08 m, about 0.005 m to about 0.07 m, about 0.005 m to about 0.06m, about 0.005 m to about 0.05 m, about 0.005 m to about 0.04 m, about0.005 m to about 0.03 m, about 0.005 m to about 0.02 m, or about 0.005 mto about 0.01 m. In some embodiments, each weir in a chamber has aheight of about 0.1 m or less, about 0.09 m or less, about 0.08 m orless, about 0.07 m or less, about 0.06 m or less, about 0.05 m or less,about 0.04 m or less, about 0.03 m or less, about 0.02 m or less, about0.01 m or less, or, in some cases, about 0.005 m or less. In someembodiments, each weir in a chamber has a height in the range of about 0m to about 0.1 m, about 0 m to about 0.09 m, about 0 m to about 0.08 m,about 0 m to about 0.07 m, about 0 m to about 0.06 m, about 0 m to about0.05 m, about 0 m to about 0.04 m, about 0 m to about 0.03 m, about 0 mto about 0.02 m, about 0 m to about 0.01 m, about 0 m to about 0.005 m,about 0.005 m to about 0.1 m, about 0.005 m to about 0.09 m, about 0.005m to about 0.08 m, about 0.005 m to about 0.07 m, about 0.005 m to about0.06 m, about 0.005 m to about 0.05 m, about 0.005 m to about 0.04 m,about 0.005 m to about 0.03 m, about 0.005 m to about 0.02 m, or about0.005 m to about 0.01 m.

In some embodiments, one or more weirs may be positioned to promote theflow of a liquid across the length of the chamber in a substantiallylinear path. For example, the chamber may be selected to have across-sectional shape having a length that is greater than its width(e.g., a substantially rectangular cross-section), such that the weirspromote flow of liquid along the length of the chamber. In some cases,it may be desirable to promote such cross flow across a chamber tomaximize the interaction, and therefore heat and/or mass transfer,between the liquid phase and the vapor phase of a condensable fluid.

The HDH apparatuses (e.g., bubble column apparatuses) described hereinmay further include one or more components positioned to facilitate,direct, or otherwise affect flow of a fluid within the apparatus. Insome embodiments, at least one chamber of at least one stage of acombined HDH apparatus may include one or more baffles positioned todirect flow of a fluid, such as a stream of the condensable fluid inliquid phase (e.g., water). In certain cases, each chamber of thecombined HDH apparatus may comprise one or more baffles. Suitablebaffles for use in embodiments described herein include plate-likearticles having, for example, a substantially rectangular shape. Bafflesmay also be referred to as barriers, dams, or the like.

The baffle, or combination of baffles, may be arranged in variousconfigurations so as to direct the flow of a liquid within the chamber.In some cases, the baffle(s) can be arranged such that liquid travels ina substantially linear path from one end of the chamber to the other endof the chamber (e.g., along the length of a chamber having asubstantially rectangular cross-section). In some cases, the baffle(s)can be arranged such that liquid travels in a non-linear path across achamber, such as a path having one or more bends or turns within thechamber. That is, the liquid may travel a distance within the chamberthat is longer than the length of the chamber. In some embodiments, oneor more baffles may be positioned along a bottom surface of at least onechamber within a combined HDH apparatus, thereby affecting the flow ofliquid that enters the chamber.

In some embodiments, a baffle may be positioned in a manner so as todirect flow of a liquid within a single chamber, e.g., along a bottomsurface of a chamber in either a linear or non-linear manner. In someembodiments, one or more baffles may be positioned substantiallyparallel to the transverse sides (i.e., width) of a chamber having asubstantially rectangular cross-sectional shape, i.e., may be atransverse baffle. In some embodiments, one or more baffles may bepositioned substantially parallel to the longitudinal sides (i.e.,length) of a chamber having a substantially rectangular cross-sectionalshape, i.e., may be a longitudinal baffle. In such configurations, oneor more longitudinal baffles may direct the flow of liquid along asubstantially non-linear path.

In some embodiments, one or more baffles may be positioned in a mannerso as to direct flow of a liquid within a single chamber along a paththat may promote efficiency of heat and/or mass transfer. For example, achamber may comprise a liquid entering through a liquid inlet at a firsttemperature and a gas entering through a bubble generator at a second,different temperature. In certain cases, heat and mass transfer betweenthe liquid and the gas may be increased when the first temperatureapproaches the second temperature. One factor that may affect theability of the first temperature to approach the second temperature maybe the amount of time the liquid spends flowing through the chamber.

In some cases, it may be advantageous for portions of the liquid flowingthrough the chamber to spend substantially equal amounts of time flowingthrough the chamber. For example, heat and mass transfer may undesirablybe reduced under conditions where a first portion of the liquid spends ashorter amount of time in the chamber and a second portion of the liquidspends a longer amount of time in the chamber. Under such conditions,the temperature of a mixture of the first portion and the second portionmay be further from the second temperature of the gas than if both thefirst portion and the second portion had spent a substantially equalamount of time in the chamber. Accordingly, in some embodiments, one ormore baffles may be positioned in the chamber to facilitate liquid flowsuch that portions of the liquid flowing through the chamber spendsubstantially equal amounts of time flowing through the chamber. Forexample, one or more baffles within the chamber may spatially separateliquid located at the inlet (e.g., liquid likely to have spent a shorteramount of time in the chamber) from liquid located at the outlet (e.g.,liquid likely to have spent a longer amount of time in the chamber). Insome cases, one or more baffles within the chamber may facilitate liquidflow along flow paths having substantially the same length. For example,the one or more baffles may prevent a first portion of liquid fromtravelling along a substantially shorter path from the inlet of thechamber to the outlet of the chamber (e.g., along the width of a chamberhaving a rectangular cross section) and a second portion of liquid fromtravelling along a substantially longer path from the inlet of thechamber to the outlet of the chamber (e.g., along the length of achamber having a rectangular cross section).

In some cases, it may be advantageous to increase the amount of time aliquid spends flowing through a chamber. Accordingly, in certainembodiments, one or more baffles may be positioned within a singlechamber to facilitate liquid flow along a flow path having a relativelyhigh aspect ratio (e.g., the ratio of the average length of the flowpath to the average width of the flow path). For example, in some cases,one or more baffles may be positioned such that liquid flowing throughthe chamber follows a flow path having an aspect ratio of at least about1.5, at least about 2, at least about 5, at least about 10, at leastabout 20, at least about 50, at least about 75, at least about 100, ormore. In some embodiments, liquid flowing through the chamber follows aflow path having an aspect ratio in the range of about 1.5 to about 5,about 1.5 to about 10, about 1.5 to about 20, about 1.5 to about 50,about 1.5 to about 75, about 1.5 to about 100, about 5 to about 10,about 5 to about 20, about 5 to about 50, about 5 to about 75, about 5to about 100, about 10 to about 20, about 10 to about 50, about 10 toabout 75, about 10 to about 100, or about 50 to about 100.

In some cases, the aspect ratio of a liquid flow path through a chambermay be larger than the aspect ratio of the chamber. In certain cases,the presence of baffles to increase the aspect ratio of a liquid flowpath may facilitate the use of an apparatus having a relatively lowaspect ratio (e.g., about 1), such as an apparatus having asubstantially circular cross section. For example, FIG. 6A shows,according to some embodiments, a schematic illustration of an exemplarychamber 600 having a substantially circular cross section (e.g., bottomsurface) and a spiral baffle 602, according to some embodiments. Inoperation, liquid may enter chamber 600 through a liquid inlet (notshown) positioned at or near the center of the substantially circularcross section. The liquid may then flow along spiral baffle 602 and exitchamber 600 through a liquid outlet (not shown) positioned at the upperedge of the substantially circular cross section. While thesubstantially circular cross section of chamber 600 has an aspect ratioof about 1, the aspect ratio of the liquid flow path is substantiallygreater than 1 (e.g., approximately 4.5). As an additional example, FIG.6B shows, according to some embodiments, a schematic illustration of anexemplary chamber 600 having a substantially circular cross section(e.g., bottom surface) and comprising a first baffle 602 and a secondbaffle 604. In operation, liquid may enter chamber 600 through a liquidinlet (not shown) located in the upper left portion of the substantiallycircular cross section. The liquid may first flow in the direction ofarrow 606. The liquid may then flow around baffle 602 and flow in theopposite direction, in the direction of arrow 608. The liquid may thenflow around baffle 604 and flow in the direction of arrow 610 andsubsequently exit chamber 600 through a liquid outlet (not shown)located in the lower right portion of the substantially circular crosssection. While the aspect ratio of the circular cross section of chamber600 is about 1, the aspect ratio of the liquid flow path through chamber600 is substantially greater than 1.

In some embodiments, the baffle is a longitudinal baffle. For example, alongitudinal baffle may extend along the length of a stage, from a firstend to a second, opposing end. In some embodiments, there may be a gapbetween the longitudinal baffle and the first end and/or the second endof the stage, such that a liquid may flow around the longitudinal baffle(e.g., in a serpentine path). In some embodiments, a stage may comprisemore than one longitudinal baffle. In some embodiments, at least onelongitudinal baffle, at least two longitudinal baffles, at least threelongitudinal baffles, at least four longitudinal baffles, at least fivelongitudinal baffles, at least ten longitudinal baffles, or more, arearranged within the chamber. In some embodiments, the chamber includes1-10 longitudinal baffles, 1-5 longitudinal baffles, or, 1-3longitudinal baffles.

In some embodiments, the baffle is a transverse baffle (e.g., ahorizontal baffle). In some cases, at least one transverse baffle, atleast two transverse baffles, at least three transverse baffles, atleast four transverse baffles, at least five transverse baffles, atleast ten transverse baffles, or more, are arranged within the chamber.In some embodiments, the chamber includes 1-10 transverse baffles, 1-5transverse baffles, or, 1-3 transverse baffles.

The combined HDH apparatus (e.g., combined bubble column apparatus) maycomprise a vessel having any shape suitable for a particularapplication. In some embodiments, the vessel of the combined HDHapparatus has a cross section that is substantially circular,substantially elliptical, substantially square, substantiallyrectangular, substantially triangular, or irregularly shaped. It hasbeen recognized that it may be advantageous, in certain cases, for thevessel of a combined HDH apparatus to have a substantially circularcross section. In some cases, a vessel having a substantially circularcross section (e.g., a substantially cylindrical vessel) may be easierto manufacture than a vessel having a cross section of a different shape(e.g., a substantially rectangular cross section). For example, for asubstantially cylindrical vessel of a combined HDH apparatus having acertain diameter (e.g., about 0.6 m or less), prefabricated pipes and/ortubes may be used to form the walls of the vessel of the HDH apparatus.In addition, a substantially cylindrical vessel of a combined HDHapparatus may be manufactured from a sheet material (e.g., stainlesssteel) by bending the sheet and welding a single seam. In contrast, avessel of a combined HDH apparatus having a cross section of a differentshape may have more than one welded seam (e.g., a combined HDH apparatushaving a substantially rectangular cross section may have four weldedseams). Further, a vessel of a combined HDH apparatus having asubstantially circular cross section may require less material tofabricate than a combined HDH apparatus having a cross section of adifferent shape (e.g., a substantially rectangular cross section). Incertain embodiments, the vessel of the combined HDH apparatus has asubstantially parallelepiped shape, a substantially rectangularprismatic shape, a substantially cylindrical shape, a substantiallypyramidal shape, and/or an irregular shape. In some cases, it may beadvantageous for a vessel of a combined HDH apparatus (e.g., a combinedbubble column apparatus) to have a relatively high aspect ratio. Forexample, in some cases, it may be advantageous for a vessel of acombined HDH apparatus to have a substantially rectangular crosssection.

The vessel of the combined HDH apparatus (e.g., combined bubble columnapparatus) may have any size suitable for a particular application. Insome embodiments, the maximum cross-sectional dimension of the vessel ofthe combined HDH apparatus is about 10 m or less, about 5 m or less,about 2 m or less, about 1 m or less, about 0.5 m or less, or about 0.1m or less. In some cases, the vessel of the combined HDH apparatus has amaximum cross-sectional dimension ranging from about 0.01 m to about 10m, about 0.01 m to about 5 m, about 0.01 m to about 1 m, about 0.5 m toabout 10 m, about 0.5 m to about 5 m, about 0.5 m to about 1 m, about 1m to about 5 m, or about 1 m to about 10 m.

The exterior of the combined HDH apparatus (e.g., combined bubble columnapparatus) may comprise any suitable material. In certain embodiments,the vessel of the combined HDH apparatus comprises stainless steel,aluminum, and/or a plastic (e.g., polyvinyl chloride, polyethylene,polycarbonate). In some embodiments, it may be advantageous to minimizeheat loss from the vessel of the combined HDH apparatus to theenvironment. In some cases, the exterior and/or the interior of thevessel of the apparatus may comprise a thermally insulating material.For example, the vessel of the apparatus may be at least partiallycoated, covered, or wrapped with a thermally insulating material.Non-limiting examples of suitable thermally insulating materials includeelastomeric foam, fiberglass, ceramic fiber mineral wool, glass mineralwool, phenolic foam, polyisocyanurate, polystyrene, and polyurethane.

In certain cases, it may be advantageous for a combined HDH apparatus(e.g., a combined bubble column apparatus) to have a relatively lowheight and/or a relatively small footprint. For example, a relativelylow height and/or relatively small footprint may advantageouslyfacilitate shipping (e.g., because the apparatus may fit on existingtruck beds and/or in standard shipping containers) and/or installationof the apparatus, particularly for systems located at remote sites. Incontrast, conventional HDH systems typically are relatively tall and/orhave a relatively large footprint. For example, conventional HDH systemsoften comprise packed bed humidifiers, which are often relatively tall(e.g., at least about 20 m tall) in order to produce a sufficient amountof relatively pure water. Due to the sizes of existing shipping trailers(e.g., truck beds) and shipping containers, and due to certain highwayrestrictions (e.g., height of bridges and/or overpasses), suchhumidifiers generally need to be shipped to a deployment site in piecesand assembled at the deployment site. The need to assemble thehumidifier and/or dehumidifier at the deployment site, which is oftenremote, may increase time and monetary costs associated with deploymentof the conventional HDH systems. In addition, the relatively large sizeof the humidifier and/or dehumidifier may be necessitate additionalexpenses. For example, a humidifier and/or dehumidifier that isrelatively tall and/or has a relatively large footprint may requireconstruction of a relatively large cement foundation, assembly of asubstantial and complicated pipe rack, and/or lightning protection.Additionally, a humidifier and/or dehumidifier that is relatively talland/or has a relatively large footprint may be difficult to move todifferent sites without substantial additional expense.

According to some embodiments, the combined HDH apparatus (e.g.,combined bubble column apparatus) has a relatively low height. Forexample, in some embodiments, the combined HDH apparatus comprises avessel having a relatively low height. The height of a vessel may referto the maximum vertical distance between a first end (e.g., a top end)and a second end (e.g., a bottom end) of the vessel. Referring to FIG.1A, vessel 150 of apparatus 100 has a height H_(v). In some cases, thevessel of the combined HDH apparatus has a height of about 5 m or less,about 4 m or less, about 3.5 m or less, about 3 m or less, about 2 m orless, about 1 m or less, or, in some cases, about 0.5 m or less. Incertain cases, the vessel of the combined HDH apparatus has a height inthe range of about 1 m to about 5 m, about 1 m to about 4 m, about 1 mto about 3.5 m, about 1 m to about 3 m, or about 1 m to about 2 m. Insome cases, a combined HDH apparatus having a relatively low height(e.g., about 5 m or less) may be shipped pre-assembled and in anoperational orientation (e.g., upright) to a deployment site via ashipping trailer or shipping container. Such an apparatus may, in somecases, require minimal time and/or money to deploy in the field.

In some embodiments, the vessel of the combined HDH apparatus (e.g.,combined bubble column apparatus) has a relatively small footprint(e.g., surface area of a bottom surface of the vessel when in anoperational orientation). In certain embodiments, the vessel of thecombined HDH apparatus has a footprint of about 100 m² or less, about 75m² or less, about 50 m² or less, about 20 m² or less, about 10 m² orless, about 5 m² or less, about 2 m² or less, or about 1 m² or less. Insome cases, the vessel of the combined HDH apparatus has a footprint inthe range of about 10 m² to about 100 m², about 10 m² to about 75 m²,about 10 m² to about 50 m², about 10 m² to about 20 m², about 1 m² toabout 100 m², about 1 m² to about 75 m², about 1 m² to about 50 m²,about 1 m² to about 20 m², about 1 m² to about 10 m², or about 1 m² toabout 5 m².

In some embodiments, the vessel of the combined HDH apparatus has arelatively high maximum cross-sectional aspect ratio. As used herein,the cross-sectional aspect ratio of a vessel refers to the ratio of thelength of the vessel to the width of the vessel when in an operationalorientation. The length of the vessel refers to the largestcross-sectional dimension of the vessel measured in a planeperpendicular to a primary axis of the vessel, where the primary axis(e.g., a vertical axis, a horizontal axis) of the vessel runs parallelto the largest dimension of the vessel. The width of the vessel refersto the largest cross-sectional dimension of the vessel measuredperpendicular to the length in the plane perpendicular to the primaryaxis of the vessel. In some cases, the cross-sectional aspect ratio mayvary along the primary axis. The maximum cross-sectional aspect ratiorefers to the largest value of the cross-sectional aspect ratios. Insome embodiments, the vessel of the combined HDH apparatus has a maximumcross-sectional aspect ratio of at least about 1.5, at least about 2, atleast about 5, at least about 10, at least about 15, or at least about20. In some embodiments, the vessel of the combined HDH apparatus has amaximum cross-sectional aspect ratio in the range of about 1.5 to about5, about 1.5 to about 10, about 1.5 to about 15, about 1.5 to about 20,about 2 to about 5, about 2 to about 10, about 2 to about 15, about 2 toabout 20, about 5 to about 10, about 5 to about 15, about 5 to about 20,about 10 to about 15, about 10 to about 20, or about 15 to about 20.

In some embodiments, the combined HDH apparatus further comprisesadditional features facilitating transport of the apparatus. In certainembodiments, for example, the combined HDH apparatus comprises anintegrated wheel base. For example, FIG. 7A is a schematic illustrationof an exemplary combined HDH apparatus 700 comprising a vesselcomprising humidification region 710 and dehumidification region 720 andintegrated wheel base 730, which comprises two wheels and has aself-leveling edge (e.g., a leveling edge configured to place the bulkof the weight of the apparatus on the main frame of the apparatus ratherthan on the wheels). Exemplary combined HDH apparatus 700 may bedirectly connected to a tractor unit (not shown in FIG. 7) and may avoidthe need for a separate shipping trailer. When not connected to atractor unit (e.g., when resting on the ground), the self-leveling edgeof integrated wheel base 730 may ensure that most of the weight of theapparatus falls on the main frame of the apparatus and not on thewheels. Additional views of exemplary combined HDH apparatus 700 areshown in FIGS. 7B and 7C.

In certain embodiments, a combined HDH apparatus comprises one or moreintegrated wheels (e.g., wheels directly integrated with the apparatus).In embodiments in which the combined HDH apparatus comprises two or moreintegrated wheels, the combined HDH apparatus may further comprise oneor more axles, each axle connecting two or more wheels (e.g., two ormore integrated wheels). In some embodiments, a combined HDH apparatuscomprising one or more integrated wheels and/or one or more axles may bedirectly connected to a tractor unit.

According to some embodiments, the desalination system further comprisesa shipping trailer. In some embodiments, the vessel of the combined HDHapparatus is positioned on the shipping trailer. The shipping trailermay be any type of shipping trailer known in the art. Examples ofsuitable types of shipping trailers include, but are not limited to,flatbed trailers, extendable flatbed trailers, stepdeck trailers (alsoreferred to as dropdeck trailers), extendable stepdeck trailers (alsoreferred to as extendable dropdeck trailers), two axle spread stepdecktrailers, lowboy trailers, and extendable lowboy trailers. FIG. 8A showsa schematic illustration of an exemplary system comprising a combinedHDH apparatus 800 and a flatbed trailer 820. FIG. 8B shows a schematicillustration of an exemplary system comprising a combined HDH apparatus830 and a stepdeck trailer 840. FIG. 8C shows a schematic illustrationof an exemplary system comprising a combined HDH apparatus 850 and alowboy trailer 860. Each type of shipping trailer may have a certainamount of available shipping area (e.g., the area that may be occupiedby cargo). In some cases, the available shipping area of a flatbedtrailer may be larger than the available shipping area of a stepdecktrailer or a lowboy trailer. In certain cases, therefore, the largestcombined HDH apparatus that may be transported on a flatbed trailer maybe larger and have a higher capacity (e.g., have a higher evaporationrate and/or condensation rate) than the largest combined HDH apparatusthat may be transported on a stepdeck trailer or a lowboy trailer.

In some embodiments, the combined HDH apparatus is configured to fitwithin the dimensions of the shipping trailer. In certain embodiments,the shipping trailer has a length of about 40 feet, about 48 feet, about53 feet, or about 70 feet. In certain embodiments, the shipping trailerhas a width of about 8 feet, 6 inches. In some cases, the combined HDHapparatus is configured to occupy a relatively large percentage of theavailable shipping area of the shipping trailer. In certain embodiments,the combined HDH apparatus has a footprint that occupies at least about20%, at least about 30%, at least about 40%, at least about 50%, atleast about 60%, at least about 80%, at least about 90%, at least about95%, or about 100% of the shipping area of the shipping trailer. In someembodiments, the combined HDH apparatus has a footprint that occupiesabout 20% to about 50%, about 20% to about 60%, about 20% to about 70%,about 20% to about 80%, about 20% to about 90%, about 20% to about 100%,about 50% to about 60%, about 50% to about 70%, about 50% to about 80%,about 50% to about 90%, about 50% to about 100%, about 60% to about100%, about 70% to about 100%, about 80% to about 100%, or about 90% toabout 100% of the shipping area of the shipping trailer. In certainembodiments, the combined HDH apparatus is contoured (e.g., around awheel well of the shipping trailer) to occupy a larger percentage of theshipping area of the shipping trailer.

According to some embodiments, the desalination system further comprisesa shipping container. In some embodiments, the vessel(s) of the combinedHDH apparatus is(are) positioned in the shipping container. The shippingcontainer may be any type of shipping container known in the art. Insome embodiments, the shipping container is a 5′ container (ISOdesignation 1F, 4′ 9.5″×8′×8′, also called “Quadcon”), a 6.5′ container(ISO designation 1E, 6′ 5.5″×8′×8′, also called “Tricon”), a 10′container (ISO designation 1D, 9′ 9.75″×8′×8′, also called “Bicon”), a20′ standard container (ISO designation 1CC, 19′ 10.5″×8′×8′ 6″), a 20′container (ISO designation 1C, 19′ 10.5″×8′×8′), a 30′ high cubecontainer (ISO Designation 1BBB, 29′ 11.25″×8′×9′ 6″), a 30′ standardcontainer (ISO designation 1BB, 29′ 11.25″×8′×8′ 6″), a 30′ container(ISO designation 1B, 29′ 11.25″×8′×8′), a 40′ high cube container (ISOdesignation 1AAA, 40′×8′×9′ 6″), a 40′ standard container (ISOdesignation 1AA, 40′×8′×8′ 6″), a 40′ container (ISO designation 1A,40′×8′×8′), a 45′ high cube container (45′×8′×9′ 6″), a 45′ standardcontainer (45′×8′⊖8′ 6″), a 48′ high cube container (48′×8′ 6″×9′ 6″), a53′ container (53′×8′ 6″×9′ 6″), and/or a European pallet wide container(e.g., having an internal width of 2.44 m). The shipping container maybe an intermodal shipping container. In certain embodiments, theshipping container has a nominal length of 20 feet, 40 feet, 45 feet, 48feet, or 53 feet. In some embodiments, the shipping container has alength of 4 ft. 9.5 in., 6 ft. 5.5 in., 9 ft. 9.75 in., 19 ft. 10.5 in.,29 ft. 11.25 in., 40 ft., 45 ft., 48 ft., or 53 ft. In certainembodiments, the shipping container has a width of about 8 feet or 8feet 6 inches. In certain embodiments, the shipping container has aheight of 8 feet, 8 feet 6 inches, or 9 feet 6 inches.

In some embodiments, the combined HDH apparatus is configured to fitwithin the dimensions of the shipping container. In some cases, thecombined HDH apparatus is configured to occupy a relatively largepercentage of the available shipping area of the shipping container. Incertain embodiments, the combined HDH apparatus has a footprint thatoccupies at least about 20%, at least about 30%, at least about 40%, atleast about 50%, at least about 60%, at least about 80%, at least about90%, at least about 95%, or about 100% of the shipping area of theshipping container. In some embodiments, the combined HDH apparatus hasa footprint that occupies about 20% to about 50%, about 20% to about60%, about 20% to about 70%, about 20% to about 80%, about 20% to about90%, about 20% to about 100%, about 50% to about 60%, about 50% to about70%, about 50% to about 80%, about 50% to about 90%, about 50% to about100%, about 60% to about 100%, about 70% to about 100%, about 80% toabout 100%, or about 90% to about 100% of the shipping area of theshipping container.

In some embodiments, the combined HDH apparatus is configured to occupya relatively large percentage of the available shipping volume (e.g.,the volume that may be occupied by cargo) of the shipping container. Incertain embodiments, the combined HDH apparatus occupies at least about20%, at least about 30%, at least about 40%, at least about 50%, atleast about 60%, at least about 80%, at least about 90%, at least about95%, or about 100% of the shipping volume of the shipping container. Insome embodiments, the combined HDH apparatus occupies about 20% to about50%, about 20% to about 60%, about 20% to about 70%, about 20% to about80%, about 20% to about 90%, about 20% to about 100%, about 50% to about60%, about 50% to about 70%, about 50% to about 80%, about 50% to about90%, about 50% to about 100%, about 60% to about 100%, about 70% toabout 100%, about 80% to about 100%, or about 90% to about 100% of theshipping volume of the shipping container.

While the features described above have been discussed in the context ofcombined HDH apparatuses comprising a vessel comprising a humidificationregion and a dehumidification region, in alternative embodiments, atleast some or all of the described features (e.g., shape, aspect ratio,presence of weirs and/or baffles, etc.) may also be applied to thedesign criteria for humidifiers and/or dehumidifiers, individually, aswell as overall HDH systems comprising a coupled but physically separatehumidifier (e.g., bubble column humidifier) and dehumidifier (e.g.,bubble column condenser). In certain embodiments, an HDH apparatus maycomprise a first vessel comprising a humidifier (e.g., bubble columnhumidifier) and a second, separate vessel comprising a dehumidifier(e.g., bubble column condenser).

In some embodiments, the humidifier (e.g., bubble column humidifier)and/or dehumidifier (e.g., bubble column condenser) have a relativelylow height and/or relatively small footprint, which may advantageouslyfacilitate shipping and/or installation of the humidifier and/ordehumidifier. In some embodiments, the humidifier (e.g., bubble columnhumidifier) and/or dehumidifier (e.g., bubble column condenser) have aheight of about 5 m or less, about 4 m or less, about 3.5 m or less,about 3 m or less, about 2 m or less, about 1 m or less, or, in somecases, about 0.5 m or less. In certain cases, the humidifier and/ordehumidifier have a height in the range of about 1 m to about 5 m, about1 m to about 4 m, about 1 m to about 3.5 m, about 1 m to about 3 m, orabout 1 m to about 2 m. In some cases, a humidifier or dehumidifierhaving a relatively low height (e.g., about 5 m or less) may be shippedpre-assembled (e.g., upright) to a deployment site via a shippingtrailer or shipping container.

In some embodiments, the humidifier (e.g., bubble column humidifier)and/or dehumidifier (e.g., bubble column condenser) have a relativelysmall footprint (e.g., surface area of a bottom surface of thehumidifier or dehumidifier). In certain embodiments, the humidifierand/or dehumidifier have a footprint of about 100 m² or less, about 75m² or less, about 50 m² or less, about 20 m² or less, about 10 m² orless, about 5 m² or less, about 2 m² or less, or about 1 m² or less. Insome cases, the humidifier and/or dehumidifier have a footprint in therange of about 10 m² to about 100 m², about 10 m² to about 75 m², about10 m² to about 50 m², about 10 m² to about 20 m², about 1 m² to about100 m², about 1 m² to about 75 m², about 1 m² to about 50 m², about 1 m²to about 20 m², about 1 m² to about 10 m², or about 1 m² to about 5 m².

In some embodiments, the humidifier (e.g., bubble column humidifier)and/or dehumidifier (e.g., bubble column condenser) have a relativelyhigh maximum cross-sectional aspect ratio. In some embodiments, thehumidifier and/or dehumidifier have a maximum cross-sectional aspectratio of at least about 1.5, at least about 2, at least about 5, atleast about 10, at least about 15, or at least about 20. In certaincases, the humidifier and/or dehumidifier have a maximum cross-sectionalaspect ratio in the range of about 1.5 to about 5, about 1.5 to about10, about 1.5 to about 15, about 1.5 to about 20, about 2 to about 5,about 2 to about 10, about 2 to about 15, about 2 to about 20, about 5to about 10, about 5 to about 15, about 5 to about 20, about 10 to about15, about 10 to about 20, or about 15 to about 20.

In some embodiments, the humidifier (e.g., bubble column humidifier) isconfigured to have a relatively high evaporation rate. In certain cases,for example, the humidifier has an evaporation rate of at least about 50barrels/day, at least about 100 barrels/day, at least about 200barrels/day, at least about 500 barrels/day, at least about 1,000barrels a day, at least about 1,500 barrels/day, at least about 2,000barrels/day, at least about 3,000 barrels/day, at least about 4,000barrels/day, or at least about 5,000 barrels/day. In some embodiments,the humidifier has an evaporation rate of about 50 barrels/day to about500 barrels/day, about 50 barrels/day to about 1,000 barrels/day, about50 barrels/day to about 1,500 barrels/day, about 50 barrels/day to about2,000 barrels/day, about 50 barrels/day to about 3,000 barrels/day,about 50 barrels/day to about 4,000 barrels/day, about 50 barrels/day toabout 5,000 barrels/day, about 100 barrels/day to about 500 barrels/day,about 100 barrels/day to about 1,000 barrels/day, about 100 barrels/dayto about 1,500 barrels/day, about 100 barrels/day to about 2,000barrels/day, about 100 barrels/day to about 3,000 barrels/day, about 100barrels/day to about 4,000 barrels/day, about 100 barrels/day to about5,000 barrels/day, about 200 barrels/day to about 1,000 barrels/day,about 200 barrels/day to about 1,500 barrels/day, about 200 barrels/dayto about 2,000 barrels/day, about 200 barrels/day to about 3,000barrels/day, about 200 barrels/day to about 4,000 barrels/day, about 200barrels/day to about 5,000 barrels/day, about 500 barrels/day to about1,000 barrels/day, about 500 barrels/day to about 1,500 barrels/day,about 500 barrels/day to about 2,000 barrels/day, about 500 barrels/dayto about 3,000 barrels/day, about 500 barrels/day to about 4,000barrels/day, about 500 barrels/day to about 5,000 barrels/day, about1,000 barrels/day to about 2,000 barrels/day, about 1,000 barrels/day toabout 3,000 barrels/day, about 1,000 barrels/day to about 4,000barrels/day, about 1,000 barrels/day to about 5,000 barrels/day, about2,000 barrels/day to about 5,000 barrels/day, about 3,000 barrels/day toabout 5,000 barrels/day, or about 4,000 barrels/day to about 5,000barrels/day. The evaporation rate of the humidifier may be obtained bymeasuring the total liquid output volume of the humidifier over a timeperiod (e.g., one day) and subtracting the total liquid input volume ofthe humidifier over the same time period.

In some embodiments, the dehumidifier (e.g., bubble column condenser) isconfigured to have a relatively high condensation rate. In certaincases, for example, the dehumidifier has a condensation rate of at leastabout 50 barrels/day, at least about 100 barrels/day, at least about 200barrels/day, at least about 500 barrels/day, at least about 1,000barrels a day, at least about 1,500 barrels/day, at least about 2,000barrels/day, at least about 3,000 barrels/day, at least about 4,000barrels/day, or at least about 5,000 barrels/day. In some embodiments,the dehumidifier has a condensation rate of about 50 barrels/day toabout 500 barrels/day, about 50 barrels/day to about 1,000 barrels/day,about 50 barrels/day to about 1,500 barrels/day, about 50 barrels/day toabout 2,000 barrels/day, about 50 barrels/day to about 3,000barrels/day, about 50 barrels/day to about 4,000 barrels/day, about 50barrels/day to about 5,000 barrels/day, about 100 barrels/day to about500 barrels/day, about 100 barrels/day to about 1,000 barrels/day, about100 barrels/day to about 1,500 barrels/day, about 100 barrels/day toabout 2,000 barrels/day, about 100 barrels/day to about 3,000barrels/day, about 100 barrels/day to about 4,000 barrels/day, about 100barrels/day to about 5,000 barrels/day, about 200 barrels/day to about1,000 barrels/day, about 200 barrels/day to about 1,500 barrels/day,about 200 barrels/day to about 2,000 barrels/day, about 200 barrels/dayto about 3,000 barrels/day, about 200 barrels/day to about 4,000barrels/day, about 200 barrels/day to about 5,000 barrels/day, about 500barrels/day to about 1,000 barrels/day, about 500 barrels/day to about1,500 barrels/day, about 500 barrels/day to about 2,000 barrels/day,about 500 barrels/day to about 3,000 barrels/day, about 500 barrels/dayto about 4,000 barrels/day, about 500 barrels/day to about 5,000barrels/day, about 1,000 barrels/day to about 2,000 barrels/day, about1,000 barrels/day to about 3,000 barrels/day, about 1,000 barrels/day toabout 4,000 barrels/day, about 1,000 barrels/day to about 5,000barrels/day, about 2,000 barrels/day to about 5,000 barrels/day, about3,000 barrels/day to about 5,000 barrels/day, or about 4,000 barrels/dayto about 5,000 barrels/day. The condensation rate of the dehumidifiermay be obtained by measuring the total liquid output volume of thedehumidifier over a time period (e.g., one day) and subtracting thetotal liquid input volume of the dehumidifier over the same time period.

In some embodiments, the humidifier (e.g., bubble column humidifier)and/or dehumidifier (e.g., bubble column condenser) further compriseadditional features facilitating transport of the units to aninstallation site. In certain embodiments, for example, the humidifierand/or dehumidifier comprise an integrated wheel base. In someembodiments, the humidifier, dehumidifier, and/or integrated wheel basemay comprise a self-leveling edge (e.g., a leveling edge configured toplace the bulk of the weight of the humidifier and/or dehumidifier onthe main frame of the humidifier and/or dehumidifier and not on thewheels). In alternative embodiments, the humidifier and/or dehumidifiercomprise one or more integrated wheels. In embodiments in which thehumidifier and/or dehumidifier comprise two or more integrated wheels,the humidifier and/or dehumidifier may further comprise one or moreaxles, each axle connecting two or more wheels (e.g., two or moreintegrated wheels). The presence of the integrated wheel base and/or theone or more integrated wheels may advantageously allow the humidifierand/or dehumidifier to be transported without additional transportsupport (e.g., a shipping trailer). For example, in some cases, thehumidifier and/or dehumidifier may be directly connected to a tractorunit.

In some embodiments, the desalination system further comprises one ormore shipping trailers. In some embodiments, the humidifier (e.g.,bubble column humidifier) and dehumidifier (e.g., bubble columncondenser) are positioned on a single shipping trailer (e.g., a doubleunit shipping trailer). The shipping trailer may be any shipping trailerknown in the art. Examples of suitable shipping trailers include, butare not limited to, flatbed trailers, extendable flatbed trailers,stepdeck trailers (also referred to as dropdeck trailers), extendablestepdeck trailers (also referred to as extendable dropdeck trailers),two axle spread stepdeck trailers, lowboy trailers, and extendablelowboy trailers. In some cases, positioning the humidifier anddehumidifier on a single trailer may reduce the assembly required at adeployment site and may thereby reduce the time and monetary costsassociated with deployment of the humidifier and dehumidifier.

In some cases, the desalination system comprises two shipping trailers.In certain embodiments, for example, a humidifier (e.g., bubble columnhumidifier) may be positioned on a first shipping trailer, and adehumidifier (e.g., bubble column condenser) may be positioned on asecond shipping trailer. The first shipping trailer and second shippingtrailer may independently be any type of suitable shipping trailer.Non-limiting examples of suitable shipping trailers include flatbedtrailers, extendable flatbed trailers, stepdeck trailers (also referredto as dropdeck trailers), extendable stepdeck trailers (also referred toas extendable dropdeck trailers), two axle spread stepdeck trailers,lowboy trailers, and extendable lowboy trailers. FIG. 9A shows aschematic illustration of an exemplary system comprising a humidifier900 on a flatbed shipping trailer 915 and a dehumidifier 905 on aflatbed shipping trailer 920. FIG. 9B shows a schematic illustration ofan exemplary system comprising a humidifier 925 on a stepdeck trailer935 and a dehumidifier 930 on a stepdeck trailer 940. FIG. 9C shows aschematic illustration of an exemplary system comprising a humidifier945 on a lowboy trailer 955 and a dehumidifier 950 on a lowboy trailer960. It should be noted that although FIGS. 9A-C show the humidifier anddehumidifier of a system being transported on the same type of shippingtrailer, the humidifier and dehumidifier of a system may also betransported on different types of shipping trailers (e.g., a flatbedtrailer and a stepdeck trailer).

In some embodiments, the humidifier (e.g., bubble column humidifier)and/or dehumidifier (e.g., bubble column condenser) are configured tofit within the dimensions of the one or more shipping trailers. Incertain embodiments, each of the one or more shipping trailers has alength of about 48 feet or about 53 feet. In certain embodiments, eachof the one or more shipping trailers has a width of about 8 feet, 6inches. In some embodiments, the humidifier and/or dehumidifier areconfigured to occupy a relatively large percentage of the availableshipping area of one or more shipping trailers. In certain embodiments,the humidifier and/or dehumidifier have a footprint that occupies atleast about 20%, at least about 30%, at least about 40%, at least about50%, at least about 60%, at least about 80%, at least about 90%, atleast about 95%, or about 100% of the shipping area of the one or moreshipping trailers. In some embodiments, the humidifier and/ordehumidifier have a footprint that occupies about 20% to about 50%,about 20% to about 60%, about 20% to about 70%, about 20% to about 80%,about 20% to about 90%, about 20% to about 100%, about 50% to about 60%,about 50% to about 70%, about 50% to about 80%, about 50% to about 90%,about 50% to about 100%, about 60% to about 100%, about 70% to about100%, about 80% to about 100%, or about 90% to about 100% of theshipping area of the one or more shipping trailers. In certainembodiments, the humidifier and/or dehumidifier are contoured (e.g.,around a wheel well of the shipping trailer) to occupy a largerpercentage of the shipping area of the one or more shipping trailers.

According to some embodiments, the desalination system further comprisesone or more shipping containers. In some embodiments, the humidifier(e.g., bubble column humidifier) and dehumidifier (e.g., bubble columncondenser) may be positioned in a single shipping container. Theshipping container may be any type of shipping container known in theart. In certain cases, for example, the shipping container may be anintermodal shipping container.

In some embodiments, the desalination system comprises two shippingcontainers. In certain embodiments, for example, a humidifier (e.g., abubble column humidifier) is positioned in a first shipping container,and a dehumidifier (e.g., a bubble column condenser) is positioned in asecond shipping container. The first shipping container and secondshipping container may independently be any type of shipping containerknown in the art. In certain embodiments, the first shipping containerand/or second shipping container are intermodal shipping containers.

The shipping container(s) may be any type of shipping container known inthe art. In some embodiments, the one or more shipping containers are a5′ container (ISO designation 1F, 4′ 9.5″×8′×8′, also called “Quadcon”),a 6.5′ container (ISO designation 1E, 6′ 5.5″×8′×8′, also called“Tricon”), a 10′ container (ISO designation 1D, 9′ 9.75″×8′×8′, alsocalled “Bicon”), a 20′ standard container (ISO designation 1CC, 19′10.5″×8′×8′ 6″), a 20′ container (ISO designation 1C, 19′ 10.5″×8′×8′),a 30′ high cube container (ISO Designation 1BBB, 29′ 11.25″×8′×9′ 6″), a30′ standard container (ISO designation 1BB, 29′ 11.25″×8′×8′ 6″), a 30′container (ISO designation 1B, 29′ 11.25″×8′×8′), a 40′ high cubecontainer (ISO designation 1AAA, 40′×8′×9′ 6″), a 40′ standard container(ISO designation 1AA, 40′×8′×8′ 6″), a 40′ container (ISO designation1A, 40′×8′×8′), a 45′ high cube container (45′×8′×9′ 6″), a 45′ standardcontainer (45′×8′×8′ 6″), a 48′ high cube container (48′×8′ 6″×9′ 6″), a53′ container (53′×8′ 6″×9′ 6″), and/or a European pallet wide container(e.g., having an internal width of 2.44 m).

In some embodiments, the humidifier (e.g., bubble column humidifier)and/or dehumidifier (e.g., bubble column condenser) are configured tofit within the dimensions of the one or more shipping containers. Incertain embodiments, the one or more shipping containers have a lengthof 4 ft. 9.5 in., 6 ft. 5.5 in., 9 ft. 9.75 in., 19 ft. 10.5 in., 29 ft.11.25 in., 40 ft., 45 ft., 48 ft., or 53 ft. In certain embodiments, theone or more shipping containers have a width of about 8 feet or 8 feet 6inches. In certain embodiments, the one or more shipping containers havea height of 8 feet, 8 feet 6 inches, or 9 feet 6 inches.

In some embodiments, the humidifier (e.g., bubble column humidifier)and/or dehumidifier (e.g., bubble column condenser) are configured tooccupy a relatively large percentage of the available shipping area ofthe one or more shipping containers. In certain embodiments, thehumidifier and/or dehumidifier have a footprint that occupies at leastabout 20%, at least about 30%, at least about 40%, at least about 50%,at least about 60%, at least about 80%, at least about 90%, at leastabout 95%, or about 100% of the shipping area of the one or moreshipping containers. In some embodiments, the humidifier and/ordehumidifier have a footprint that occupies about 20% to about 50%,about 20% to about 60%, about 20% to about 70%, about 20% to about 80%,about 20% to about 90%, about 20% to about 100%, about 50% to about 60%,about 50% to about 70%, about 50% to about 80%, about 50% to about 90%,about 50% to about 100%, about 60% to about 100%, about 70% to about100%, about 80% to about 100%, or about 90% to about 100% of theshipping area of the one or more shipping containers.

In some embodiments, the humidifier and/or dehumidifier are configuredto occupy a relatively large percentage of the available shipping volumeof the one or more shipping containers. In certain embodiments, thehumidifier and/or dehumidifier occupy at least about 20%, at least about30%, at least about 40%, at least about 50%, at least about 60%, atleast about 80%, at least about 90%, at least about 95%, or about 100%of the shipping volume of the one or more shipping containers. In someembodiments, the humidifier and/or dehumidifier about 20% to about 50%,about 20% to about 60%, about 20% to about 70%, about 20% to about 80%,about 20% to about 90%, about 20% to about 100%, about 50% to about 60%,about 50% to about 70%, about 50% to about 80%, about 50% to about 90%,about 50% to about 100%, about 60% to about 100%, about 70% to about100%, about 80% to about 100%, or about 90% to about 100% of theshipping volume of the one or more shipping containers.

Some aspects are directed to a desalination system comprising a combinedHDH apparatus (e.g., a combined bubble column apparatus) fluidicallyconnected to one or more additional devices. For example, in someembodiments, a desalination system comprises a combined HDH apparatus,as described herein, in fluid communication with a heat exchanger. Incertain cases, the heat exchanger facilitates transfer of heat from afluid stream flowing through a dehumidification region of the combinedHDH apparatus (e.g., a dehumidification region liquid outlet stream) toa fluid stream flowing through a humidification region of the combinedHDH apparatus (e.g., a humidification region liquid inlet stream). Forexample, the heat exchanger may advantageously allow energy to berecovered from a dehumidification region liquid outlet stream and usedto pre-heat a humidification region liquid inlet stream prior to entryof the humidification region liquid inlet stream into the humidificationregion of an exemplary combined HDH apparatus. This may, for example,avoid the need for an additional heating device to heat thehumidification region liquid inlet stream. Alternatively, if a heatingdevice is used, the presence of a heat exchanger to recover energy fromthe dehumidification region liquid outlet stream may reduce the amountof heat required to be applied to the humidification region liquid inletstream. The system can be configured such that the cooleddehumidification region liquid outlet stream can be returned to thedehumidification region through a liquid inlet and be re-used as aliquid to form liquid layers in the stage(s) of the dehumidificationregion. In this manner, the temperature of the liquid layers within thedehumidification region of the combined HDH apparatus can be regulatedsuch that, in each stage, the temperature of the liquid layer ismaintained at a temperature lower than the temperature of the gas.

In some embodiments, the heat exchanger is an external heat exchanger(e.g., external to the vessel of the combined HDH apparatus). In somecases, an external heat exchanger may be associated with certainadvantages. For example, the use of an external heat exchanger with acombined HDH apparatus may advantageously allow the apparatus to havereduced dimensions and/or reduced liquid layer heights within one ormore stages of a humidification region and/or dehumidification region ofthe apparatus. In some embodiments, the heat exchanger is an internalheat exchanger. For example, the internal heat exchanger may comprise atube coil located within a dehumidification region of a combined bubblecolumn apparatus. The tube coil may be positioned such that at least aportion of the tube coil is in thermal contact with a liquid layerwithin a stage of the dehumidification region. For example, in adehumidification region (e.g., bubble column dehumidification region)comprising a plurality of stages, each stage comprising a liquid layer,the tube coil may be positioned such that each liquid layer is inthermal contact with at least a portion of the tube coil. In some cases,a coolant (e.g., a humidification region liquid inlet stream) may flowthrough the internal heat exchanger (e.g., the tube coil), and heat maybe transferred from the liquid layer(s) of the dehumidification regionto the coolant.

FIG. 10A shows a schematic diagram of an exemplary embodiment ofdesalination system 1000 comprising combined HDH (e.g. bubble column)apparatus 1002 and external heat exchanger 1008. Combined HDH apparatus1002 may comprise vessel 1014 comprising humidification region 1004 anddehumidification region 1006. As shown in FIG. 10A, dehumidificationregion 1006 is fluidically connected to external heat exchanger 1008through liquid conduit 1010. In some cases, humidification region 1004is fluidically connected to external heat exchanger 1008 through liquidconduit 1012. It should be noted that in certain embodiments,humidification region 1004 is not connected to external heat exchanger1008, and an external cooling fluid may flow through heat exchanger 1008instead.

In operation, a dehumidification region liquid outlet stream containingan amount of absorbed heat may exit dehumidification region 1006 viaconduit 1010 at a temperature T₁ and enter external heat exchanger 1008,flowing in a first direction. A humidification region liquid outletstream may exit humidification region 1004 via conduit 1012 at atemperature T₂ and enter external heat exchanger 1008, flowing in asecond direction that is substantially opposite to the first direction(e.g., counter-flow). Heat may be transferred from the dehumidificationregion liquid stream to the humidification region liquid stream withinheat exchanger 1008. The dehumidification region liquid stream may thenexit heat exchanger 1008 at a temperature T₃, where T₃ is less than T₁,and the humidification region liquid stream may exit heat exchanger 1008at a temperature T₄, where T₄ is greater than T₂. In some cases, thehumidification region liquid stream and dehumidification region liquidstream may flow in substantially parallel directions through heatexchanger 1008. In other embodiments, the humidification region liquidstream and dehumidification region liquid stream may flow insubstantially non-parallel directions (e.g., opposite) directionsthrough heat exchanger 1008.

As noted above, in some embodiments, humidification region 1004 is notfluidically connected to heat exchanger 1008. In addition, although FIG.10A shows liquid conduit 1012 fluidically connecting an outlet ofhumidification region 1004, heat exchanger 1008, and an inlet ofhumidification region 1004, such that a stream exits humidificationregion 1004, flows through heat exchanger 1008, and returns tohumidification region 1004, in some cases, system 1000 is insteadconfigured such that heat exchanger 1008 is fluidically connected to asource of a liquid comprising one or more contaminants (not shown). Insome cases, liquid exiting humidification region 1004 does not flowthrough heat exchanger 1008.

Any heat exchanger known in the art may be used. Examples of suitableheat exchangers include, but are not limited to, plate-and-frame heatexchangers, shell-and-tube heat exchangers, tube-and-tube heatexchangers, plate heat exchangers, plate-and-shell heat exchangers,spiral heat exchangers, and the like. In a particular embodiment, theheat exchanger is a plate-and-frame heat exchanger. The heat exchangermay be configured such that a first fluid stream and a second fluidstream flow through the heat exchanger. In some cases, the first fluidstream and the second fluid stream may flow in substantially the samedirection (e.g., parallel flow), substantially opposite directions(e.g., counter flow), or substantially perpendicular directions (e.g.,cross flow). The first fluid stream may comprise, in certain cases, afluid stream that flows through a dehumidification region (e.g., adehumidification region liquid stream). In some embodiments, the secondfluid stream may comprise a coolant. The first fluid stream and/or thesecond fluid stream may comprise a liquid. In some embodiments, the heatexchanger may be a liquid-to-liquid heat exchanger. In some cases, morethan two fluid streams may flow through the heat exchanger.

The coolant may be any fluid capable of absorbing and transferring heat.Typically, the coolant is a liquid. The coolant may, in someembodiments, include water. In certain cases, the coolant may includesalt-containing water. For example, in a humidification-dehumidificationsystem, the coolant stream in the heat exchanger may be used to preheatsalt-containing water prior to entry into a humidification region (e.g.,the coolant stream may comprise the humidification region liquid inletstream).

In some embodiments, the heat exchanger may exhibit relatively high heattransfer rates. In some embodiments, the heat exchanger may have a heattransfer coefficient of at least about 150 W/(m² K), at least about 200W/(m² K), at least about 500 W/(m² K), at least about 1000 W/(m² K), atleast about 2000 W/(m² K), at least about 3000 W/(m² K), at least about4000 W/(m² K), at least about 5000 W/(m² K), at least about 6000 W/(m²K), at least about 7000 W/(m² K), at least about 8000 W/(m² K), at leastabout 9000 W/(m² K), or at least about 10,000 W/(m² K). In someembodiments, the heat exchanger may have a heat transfer coefficient inthe range of at least about 150 W/(m² K) to at least about 5000 W/(m²K), at least about 200 W/(m² K) to about 5000 W/(m² K), at least about500 W/(m² K) to about 5000 W/(m² K), at least about 1000 W/(m² K) toabout 5000 W/(m² K), at least about 2000 W/(m² K) to about 5000 W/(m²K), at least about 3000 W/(m² K) to about 5000 W/(m² K), at least about4000 W/(m² K) to about 5000 W/(m² K), about 150 W/(m² K) to about 10,000W/(m² K), about 200 W/(m² K) to about 10,000 W/(m² K), about 500 W/(m²K) to about 10,000 W/(m² K), about 1000 W/(m² K) to about 10,000 W/(m²K), about 2000 W/(m² K) to about 10,000 W/(m² K), about 3000 W/(m² K) toabout 10,000 W/(m² K), about 4000 W/(m² K) to about 10,000 W/(m² K),about 5000 W/(m² K) to about 10,000 W/(m² K), about 6000 W/(m² K) toabout 10,000 W/(m² K), about 7000 W/(m² K) to about 10,000 W/(m² K),about 8000 W/(m² K) to about 10,000 W/(m² K), or about 9000 W/(m² K) toabout 10,000 W/(m² K).

In some embodiments, the heat exchanger may increase the temperature ofone or more fluid streams (e.g., the humidification region liquid inletstream) flowing through the heat exchanger and/or decrease thetemperature of one or more fluid streams (e.g., the dehumidificationregion liquid outlet stream) flowing through the heat exchanger. Forexample, the difference between the temperature of a fluid entering theheat exchanger and the fluid exiting the heat exchanger may be at leastabout 5° C., at least about 10° C., at least about 15° C., at leastabout 20° C., at least about 30° C., at least about 40° C., at leastabout 50° C., at least about 60° C., at least about 70° C., at leastabout 80° C., at least about 90° C., or at least about 100° C. In someembodiments, the difference between the temperature of a fluid enteringthe heat exchanger and the fluid exiting the heat exchanger may be inthe range of about 5° C. to about 20° C., about 5° C. to about 30° C.,about 5° C. to about 50° C., about 5° C. to about 60° C., about 5° C. toabout 90° C., about 5° C. to about 100° C., about 10° C. to about 30°C., about 10° C. to about 60° C., about 10° C. to about 90° C., about10° C. to about 100° C., about 20° C. to about 60° C., about 20° C. toabout 90° C., about 20° C. to about 100° C., about 30° C. to about 60°C., about 30° C. to about 90° C., about 30° C. to about 100° C., about60° C. to about 90° C., about 60° C. to about 100° C., or about 80° C.to about 100° C.

In some embodiments, an optional external heating device may be arrangedin fluid communication with the combined HDH apparatus (e.g., combinedbubble column apparatus) and/or the external heat exchanger. In certaincases, the heating device may be arranged such that, in operation, aliquid stream (e.g., a heat exchanger outlet stream, a humidificationregion liquid inlet stream) is heated in the heating device prior toentering the humidification region of the combined HDH apparatus. Insome embodiments, the heating device may be arranged such that adehumidification region liquid outlet stream is heated in the heatingdevice prior to entering the heat exchanger. Such an arrangement mayadvantageously increase the amount of heat transferred from thedehumidification region liquid outlet stream to another fluid streamflowing through the heat exchanger (e.g., a humidification region liquidinlet stream).

The heating device may be any device that is capable of transferringheat to a fluid stream. In some cases, the heating device is a heatexchanger. Any heat exchanger known in the art may be used. Examples ofsuitable heat exchangers include, but are not limited to,plate-and-frame heat exchangers, shell-and-tube heat exchangers,tube-and-tube heat exchangers, plate heat exchangers, plate-and-shellheat exchangers, and the like. In a particular embodiment, the heatexchanger is a plate-and-frame heat exchanger. The heat exchanger may beconfigured such that a first fluid stream and a second fluid stream flowthrough the heat exchanger. In some cases, the first fluid stream andthe second fluid stream may flow in substantially the same direction(e.g., parallel flow), substantially opposite directions (e.g., counterflow), or substantially perpendicular directions (e.g., cross flow). Thefirst fluid stream and/or the second fluid stream may comprise a liquid.In some embodiments, the heating device is a liquid-to-liquid heatexchanger. The first fluid stream may, in some cases, comprise a fluidstream that flows through a humidification region (e.g., ahumidification region liquid inlet stream) and/or a fluid stream thatflows through a dehumidification region (e.g., a dehumidification regionliquid outlet stream). The second fluid stream may, in some cases,comprise a heating fluid. The heating fluid may be any fluid capable ofabsorbing and transferring heat. In some embodiments, the heating fluidcomprises water (e.g., hot, pressurized water). In certain embodiments,heat may be transferred from the second fluid stream (e.g., the heatingfluid) to the first stream (e.g., the humidification region liquid inletstream, the dehumidification liquid outlet stream) in the heatexchanger. In some cases, more than two fluid streams may flow throughthe heat exchanger.

In some embodiments, the heating device is a heat collection device. Theheat collection device may be configured to store and/or utilize thermalenergy (e.g., in the form of combustion of natural gas, solar energy,waste heat from a power plant, or waste heat from combusted exhaust). Incertain cases, the heating device is configured to convert electricalenergy to thermal energy. For example, the heating device may be anelectric heater.

The heating device may, in some cases, increase the temperature of oneor more fluid streams (e.g., humidification region liquid inlet stream,dehumidification region liquid outlet stream) flowing through theheating device. For example, the difference between the temperature of afluid entering the heating device and the fluid exiting the heatingdevice may be at least about 5° C., at least about 10° C., at leastabout 15° C., at least about 20° C., at least about 30° C., at leastabout 40° C., at least about 50° C., at least about 60° C., at leastabout 70° C., at least about 80° C., or, in some cases, at least about90° C. In some embodiments, the difference between the temperature of afluid entering the heating device and the fluid exiting the heatingdevice may be in the range of about 5° C. to about 30° C., about 5° C.to about 60° C., about 5° C. to about 90° C., about 10° C. to about 30°C., about 10° C. to about 60° C., about 10° C. to about 90° C., about20° C. to about 60° C., about 20° C. to about 90° C., about 30° C. toabout 60° C., about 30° C. to about 90° C., or about 60° C. to about 90°C. In some cases, the temperature of a fluid stream (e.g.,humidification region liquid inlet stream, dehumidification regionliquid outlet stream) being heated in the heating device remains belowthe boiling point of the fluid stream.

In some embodiments, a desalination system may comprise two or moreheating devices. For example, in some embodiments, a first heatingdevice further heats a humidification region liquid inlet stream afterthe stream has flowed through a heat exchanger. In some embodiments, asecond heating device heats a dehumidification region liquid outletstream prior to the stream flowing through the heat exchanger. In someembodiments, the second heating device heats the humidification regionliquid inlet stream and the first heating device heats thedehumidification region liquid outlet stream. In some embodiments, asingle heating device may function as the first heating device andsecond heating device and heat both the humidification region liquidinput stream and the dehumidification region liquid outlet stream.Further, there may be any number of heating devices present in thedesalination system.

In some embodiments, an optional external cooling device may be arrangedin fluid communication with the combined HDH apparatus (e.g., combinedbubble column apparatus) and/or the external heat exchanger. In certaincases, the cooling device may be arranged such that, in operation, aheat exchanger outlet stream (e.g., a cooled dehumidification regionliquid outlet stream) is further cooled in the cooling device prior toreturning to the combined HDH apparatus (e.g., the dehumidificationregion of the combined HDH apparatus).

A cooling device generally refers to any device that is capable ofremoving heat from a fluid stream (e.g., a liquid stream, a gas stream).In some embodiments, the cooling device is a heat exchanger. The heatexchanger may be configured such that a first fluid stream and a secondfluid stream flow through the heat exchanger. In some cases, the firstfluid stream and the second fluid stream may flow in substantially thesame direction (e.g., parallel flow), substantially opposite directions(e.g., counter-flow), or substantially perpendicular directions (e.g.,cross flow). In some cases, heat is transferred from a first fluidstream to a second fluid stream. In certain embodiments, the coolingdevice is a liquid-to-gas heat exchanger. The first fluid stream may, incertain cases, comprise a fluid stream that is part of a loop ofcondenser liquid flowing between a condenser and a heat exchanger (e.g.,a dehumidification region liquid outlet stream). The second fluid streammay, in some cases, comprise a coolant. The coolant may be any fluidcapable of absorbing or transferring heat. In some embodiments, thecoolant comprises a gas. The gas may, in some cases, comprise air (e.g.,ambient air). Heat exchangers that comprise air as a coolant maygenerally be referred to as air-cooled heat exchangers. In some cases,more than two fluid streams flow through the cooling device. It shouldalso be noted that the cooling device may, in some embodiments, be a drycooler, a chiller, a radiator, or any other device capable of removingheat from a fluid stream.

The cooling device may, in some cases, decrease the temperature of afluid stream (e.g., a heat exchanger outlet stream, a dehumidificationregion liquid outlet stream). In some embodiments, the cooling devicedecreases the temperature of the fluid stream by at least about 5° C.,at least about 10° C., at least about 15° C., at least about 20° C., atleast about 30° C., at least about 40° C., at least about 50° C., atleast about 60° C., at least about 70° C., at least about 80° C., or, insome cases, at least about 90° C. In some embodiments, the coolingdevice decreases the temperature of the fluid stream by an amount in therange of about 5° C. to about 30° C., about 5° C. to about 60° C., about5° C. to about 90° C., about 10° C. to about 30° C., about 10° C. toabout 60° C., about 10° C. to about 90° C., about 20° C. to about 30°C., about 20° C. to about 60° C., about 20° C. to about 90° C., about30° C. to about 60° C., about 30° C. to about 90° C., or about 60° C. toabout 90° C.

FIG. 7B shows an exemplary embodiment of a system 700 comprising acombined HDH (e.g. bubble column) apparatus 702, an external heatexchanger 708, an external heating device 714, and an external coolingdevice 716. Humidification region 704, heat exchanger 708, and heatingdevice 714 are arranged to be in fluid communication with each otherthrough liquid conduit 712. Dehumidification region 706, heat exchanger708, and cooling device 716 are arranged to be in fluid communicationwith each other through liquid conduit 710.

In operation, in an exemplary embodiment, a humidification region liquidoutlet stream may exit humidification region 704 at a temperature T₁ andenter heat exchanger 708, and a dehumidification region liquid outletstream may exit dehumidification region 706 at a temperature T₂ and alsoenter heat exchanger 708. In some embodiments, the humidification regionliquid outlet stream and the dehumidification region liquid outletstream may flow through heat exchanger 708 in substantially oppositedirections (e.g., heat exchanger 708 is a counter-flow heat exchanger).As the humidification region liquid outlet stream and dehumidificationregion liquid outlet stream flow through heat exchanger 708, heat may betransferred from the dehumidification region liquid outlet stream to thehumidification region liquid outlet stream, such that the temperature ofthe humidification region liquid outlet stream is increased to atemperature T₃ greater than temperature T₁, and the temperature of thedehumidification region liquid outlet stream is decreased to atemperature T₄ lower than temperature T₂. The heated humidificationregion liquid outlet stream may then exit heat exchanger 708 and flowthrough heating device 714 to be further heated, with the temperature ofthe stream increasing from temperature T₃ to a temperature T₅, which isgreater than temperature T₃. The further heated humidification regionliquid outlet stream may then be returned to humidification region 704.Optionally, a first portion of the further heated humidification regionliquid outlet stream may be returned to humidification region 704, and asecond portion may be discharged from the system and/or routed toanother portion of the system. The cooled dehumidification region liquidoutlet stream may exit heat exchanger 708 and flow through coolingdevice 716 to be further cooled, with the temperature of the streamdecreasing from temperature T₄ to a temperature T₆, which is lower thantemperature T₄. The further cooled dehumidification region liquid outletstream may then be returned to dehumidification region 706.

In some embodiments, the desalination system may be fluidicallyconnected to one or more additional devices. For example, thedesalination system may be fluidically connected to an optionalpre-treatment system and/or an optional precipitation apparatus. In somecases, a pre-treatment system may be configured to remove one or morecomponents from a liquid feed stream entering the desalination system.In some cases, a precipitation apparatus may be configured toprecipitate one or more solid salts from a liquid output stream of thedesalination system comprising one or more dissolved salts.

FIG. 11 is a schematic diagram of exemplary system 1100, according tocertain embodiments. In FIG. 11, system 1100 comprises optionalpretreatment system 1102, desalination system 1116, and optionalprecipitation apparatus 1118. As shown in FIG. 11, pretreatment system1102 comprises optional separation apparatus 1104 configured to removeat least a portion of a suspended and/or emulsified immiscible phasefrom a liquid stream, optional ion-removal apparatus 1106 configured toremove at least a portion of at least one scale-forming ion from aliquid stream, optional suspended solids removal apparatus 1108configured to remove at least a portion of suspended solids from aliquid stream, optional pH adjustment apparatus 1110 configured toadjust (i.e. increase or decrease) or maintain/stabilize (e.g. viabuffering) the pH of a liquid stream, optional volatile organic material(VOM) removal apparatus 1112 configured to remove at least a portion ofVOM from a liquid stream, and/or optional filtration apparatus 1114configured to produce a substantially solid material. Each component ofsystem 1100 may be fluidically connected to one or more other componentsof system 1100, either directly or indirectly. It should be noted thateach of the components of system 1100 shown in FIG. 11 is optional, anda system may comprise any combination of the components shown in FIG.11. In some embodiments, desalination system 1100 further comprises oneor more feed tanks and/or one or more storage tanks (e.g., a tank tostore substantially pure water) (not shown in FIG. 11).

In operation, liquid feed stream 1120 comprising a suspended and/oremulsified immiscible phase, a scale-forming ion, suspended solids,and/or a volatile organic material is flowed to separation apparatus1104. Separation apparatus 1104 removes at least a portion of thesuspended and/or emulsified immiscible phase to produceimmiscible-phase-diminished stream 1122, which contains less of theimmiscible phase than stream 1120. In certain embodiments, separationapparatus 1104 also produces immiscible-phase-enriched stream 1124,which contains more of the immiscible phase than stream 1120.Immiscible-phase-diminished stream 1122 is then made to flow toion-removal apparatus 1106. Ion-removal apparatus 1106 removes at leasta portion of at least one scale-forming ion from stream 1122 to produceion-diminished stream 1126, which contains less of at least onescale-forming ion than immiscible-phase-diminished stream 1122. Incertain embodiments, ion-removal apparatus 1106 also producesion-enriched stream 1128, which contains more of at least onescale-forming ion than immiscible-phase-diminished stream 1122.Ion-diminished stream 1126 is then made to flow to suspended solidsremoval apparatus 1108. Suspended solids removal apparatus 1108 removesat least a portion of suspended solids from ion-diminished stream 1126to produce suspended-solids-diminished stream 1130, which contains lesssuspended solids than ion-diminished stream 1126. Optionally, suspendedsolids removal apparatus 1108 may also produce suspended-solids-enrichedstream 1132, which may be flowed to filtration apparatus 1114 to formsolid stream 1134 and filtered liquid stream 1136.Suspended-solids-diminished stream 1130 is then made to flow to pHadjustment apparatus 1110. pH adjustment apparatus 1110 may, in certaincases, increase or decrease the pH of stream 1130 to produce stream1138. In some cases, chemicals 1140 (e.g., one or more acids) may beadded in pH adjustment apparatus 1110 to adjust (e.g., increase ordecrease) or maintain/stabilize (e.g., via buffering) the pH of stream1130. pH-adjusted stream 1138 is then made to flow to VOM removalapparatus 1112. VOM removal apparatus 1112 may remove at least a portionof VOM from pH-adjusted stream 1138 to produce VOM-diminished stream1142. VOM removal apparatus 1112 may also produce VOM-enriched stream1144. VOM-diminished stream 1142 is then made to flow to desalinationsystem 1116, which may be configured to remove at least a portion of atleast one dissolved salt from VOM-diminished stream 1142. In some cases,desalination system 1116 is configured to produce a substantially purewater stream 1146 and a concentrated brine stream 1148. In certainembodiments, at least a portion of substantially pure water stream 1146is discharged from system 1100 and/or is recycled and returned todesalination system 1116. In certain cases, at least a portion ofconcentrated brine stream 1148 is made to flow to precipitationapparatus 1118. Precipitation apparatus 1118 may be configured such thatat least a portion of the dissolved salt within concentrated brinestream 1148 is precipitated within precipitation apparatus 1118 toproduce solid stream 1150 and water-containing stream 1152, whichcontains less dissolved salt than concentrated brine stream 1148.

In some cases, the precipitation apparatus comprises a vessel, such as asettling tank. The vessel may include an inlet through which at least aportion of a concentrated saline stream (e.g., a humidification regionliquid outlet stream) produced by the desalination system is transportedinto the precipitation vessel. The precipitation vessel may also includeat least one outlet. For example, the precipitation vessel may includean outlet through which a water-containing stream (containing adissolved salt in an amount that is less than that contained in theinlet stream) is transported. In some embodiments, the precipitationvessel includes an outlet through which solid, precipitated salt istransported.

In some embodiments, the settling tank comprises a low shear mixer. Thelow shear mixer can be configured to keep the crystals that are formedmixed (e.g., homogeneously mixed) in the concentrated saline stream.According to certain embodiments, the vessel is sized such that there issufficient residence time for crystals to form and grow. In certainembodiments, the precipitation apparatus comprises a vessel whichprovides at least 20 minutes of residence time for the concentratedsaline stream. As one non-limiting example, the vessel comprises,according to certain embodiments, a 6000 gallon vessel, which can beused to provide 24 minutes of residence in a 500 U.S. barrel per dayfresh water production system.

Those of ordinary skill in the art are capable of determining theresidence time of a volume of fluid in a vessel. For a batch (i.e.,non-flow) system, the residence time corresponds to the amount of timethe fluid spends in the vessel. For a flow-based system, the residencetime is determined by dividing the volume of the vessel by thevolumetric flow rate of the fluid through the vessel.

In some embodiments, the precipitation apparatus comprises at least onevessel comprising a volume within which the concentrated saline streamis substantially quiescent. In some embodiments, the flow velocity ofthe fluid within the substantially quiescent volume is less than theflow velocity at which precipitation (e.g., crystallization) isinhibited. For example, the fluid within the substantially quiescentvolume may have, in certain embodiments, a flow velocity of zero. Insome embodiments, the fluid within the substantially quiescent volumemay have a flow velocity that is sufficiently high to suspend the formedsolids (e.g., crystals), but not sufficiently high to prevent solidformation (e.g., crystal nucleation). The substantially quiescent volumewithin the vessel may occupy, in some embodiments, at least about 1%, atleast about 5%, at least about 10%, or at least about 25% of the volumeof the vessel. As one particular example, the precipitation apparatuscan comprise a vessel including a stagnation zone. The stagnation zonemay be positioned, for example, at the bottom of the precipitationvessel. In certain embodiments, the precipitation apparatus can includea second vessel in which the solids precipitated in the first vessel areallowed to settle. For example, an aqueous stream containing theprecipitated solids can be transported to a settling tank, where thesolids can be allowed to settle. The remaining contents of the aqueousstream can be transported out of the settling tank. While the use of twovessels within the precipitation apparatus has been described, it shouldbe understood that, in other embodiments, a single vessel, or more thantwo vessels may be employed. In certain embodiments, the desalinationsystem can be operated such that precipitation of the salt occurssubstantially only within the stagnation zone of the precipitationvessel.

In some embodiments, the precipitated salt from the precipitationapparatus is fed to a solids-handling apparatus. The solids-handlingapparatus may be configured, in certain embodiments, to remove at leasta portion of the water retained by the precipitated salt. In some suchembodiments, the solids-handling apparatus is configured to produce acake comprising at least a portion of the precipitated salt from theprecipitation apparatus. As one example, the solids-handling apparatuscan comprise a filter (e.g., a vacuum drum filter or a filter press)configured to at least partially separate the precipitated salt from theremainder of a suspension containing the precipitated salt. In some suchembodiments, at least a portion of the liquid within the salt suspensioncan be transported through the filter, leaving behind solid precipitatedsalt. As one non-limiting example, a Larox FP 2016-8000 64/64 M40 PP/PPFilter (Outotec, Inc.) may be used as the filter. The filter maycomprise, in certain embodiments, a conveyor filter belt which filtersthe salt from a suspension containing the salt.

It should be noted that while the combined HDH apparatuses describedherein have generally been discussed in the context of desalinationsystems, the apparatuses may be used in other types of systems (e.g.,other water treatment/purification systems). For example, the combinedHDH apparatuses may be used in separation processes to separate one ormore components of an input liquid stream (e.g., a liquid mixture). In aparticular, non-limiting embodiment, the combined HDH apparatuses may beused in distillation systems to distill certain liquids from liquidmixtures (e.g., ionic solutions). Examples of liquids that may bedistilled from liquid mixtures using the combined HDH apparatusesdescribed herein include, but are not limited to, ammonia, benzene,toluene, phenol, xylene, naphthalene, xylene, gasoline, methanol,ethanol, propanol, butanol, isopropyl alcohol, propylene glycol,hexane-n, heptane-n, octane-n, cyclohexane, acetic acid, formic acid,nitric acid, carbon tetrachloride, methyl acetate, and/or acetone.

Various of the components described herein can be “directly fluidicallyconnected” to other components. As used herein, a direct fluidconnection exists between a first component and a second component (andthe two components are said to be “directly fluidically connected” toeach other) when they are fluidically connected to each other and thecomposition of the fluid does not substantially change (i.e., no fluidcomponent changes in relative abundance by more than 5% and no phasechange occurs) as it is transported from the first component to thesecond component. As an illustrative example, a stream that connectsfirst and second system components, and in which the pressure andtemperature of the fluid is adjusted but the composition of the fluid isnot altered, would be said to directly fluidically connect the first andsecond components. If, on the other hand, a separation step is performedand/or a chemical reaction is performed that substantially alters thecomposition of the stream contents during passage from the firstcomponent to the second component, the stream would not be said todirectly fluidically connect the first and second components.

Other examples of HDH systems are described in U.S. Pat. No. 8,292,272,by Elsharqawy et al., issued Oct. 23, 2012, entitled “Water SeparationUnder Reduced Pressure”; U.S. Pat. No. 8,465,006, by Elsharqawy et al.,issued Jun. 18, 2013, entitled “Separation of a Vaporizable ComponentUnder Reduced Pressure”; U.S. Pat. No. 8,252,092, by Govindan et al.,issued Aug. 28, 2012, entitled “Water Separation Under Varied Pressure”;U.S. Pat. No. 8,496,234, by Govindan et al., issued Jul. 30, 2013,entitled “Thermodynamic Balancing of Combined Heat and Mass ExchangeDevices”; U.S. Pat. No. 8,523,985, by Govindan et al., issued Sep. 3,2013, entitled “Bubble-Column Vapor Mixture Condenser”; U.S. Pat. No.8,778,065, by Govindan et al., issued Jul. 15, 2014, entitled“Humidification-Dehumidification System Including a Bubble-Column VaporMixture Condenser”; U.S. Pat. No. 9,072,984, by Govindan et al., issuedJul. 7, 2015, entitled “Bubble-Column Vapor Mixture Condenser”; U.S.Patent Publication No. 2015/0129410, by Govindan et al., filed Sep. 12,2014, entitled “Systems Including a Condensing Apparatus Such as aBubble Column Condenser”; and International Patent Publication No. WO2014/200829, by Govindan et al., filed Jun. 6, 2014, as InternationalPatent Application No. PCT/US2014/041226, and entitled “Multi-StageBubble Column Humidifier,” the contents of all of which are incorporatedherein by reference in their entireties for all purposes.

Also disclosed are inventive methods of operating, controlling, and/orcleaning a desalination system comprising a plurality of desalinationunits (e.g., HDH desalination units). Certain embodiments, for example,relate to methods of detecting and removing scale from a desalinationsystem comprising a plurality of desalination units (e.g., HDHdesalination units). In some embodiments, at least some or all of theplurality of desalination units are mobile HDH desalination units (e.g.,HDH desalination units having a relatively low height and/or arelatively small footprint, as described above). In some cases, adesalination system comprising a plurality of mobile HDH desalinationunits may require less time and/or money to install at a deployment sitethan a desalination system comprising a single large-capacitydesalination unit. For example, in certain cases, each mobile HDHdesalination unit may be transported to a deployment site via a shippingtrailer and/or shipping container and may require only connection(s)(e.g., fluidic, electronic, and/or electrical connections) to one ormore other components (e.g., other mobile HDH desalination units, acentral feed tank, a common heating fluid source, a power source) of thedesalination system in order to operate. In contrast, a singlelarge-capacity desalination unit may need to be shipped to a deploymentsite in pieces and may need to be assembled/constructed at thedeployment site, which may increase the time and monetary costsassociated with system deployment. In addition, a desalination systemcomprising a plurality of desalination units may advantageously havemore operational flexibility than a desalination system comprising asingle large-capacity desalination unit. For example, in a desalinationsystem comprising a plurality of desalination units, one or moredesalination units may be taken offline (e.g., to be cleaned and/orrepaired) while one or more desalination units continue to operate,thereby allowing substantially continuous operation of the desalinationsystem (and, therefore, production of desalinated water). In contrast,in a desalination system comprising a single large-capacity desalinationunit, cleaning and/or repair of the desalination unit may interruptoperation of the desalination system.

There may be challenges associated with identifying a particulardesalination unit of a plurality of desalination units that is fouled(e.g., with scale) and should be cleaned (e.g., by flowing a de-scalingcomposition through at least a portion of the desalination unit). Forexample, as described in further detail below, it may be challenging topredict when scale will begin forming within a desalination unit.However, according to certain inventive methods described herein, acontrol system (e.g., an automated feedback control system)electronically connected to some or all of the plurality of desalinationunits may monitor one or more measurements (e.g., temperature and/orflow rate measurements) of the desalination units. In some cases, thecontrol system may determine a certain value (e.g., an average value, arelative standard deviation) and may identify a fouled fluidic pathwaywithin a desalination unit based on the value. In some cases, uponidentification of a fouled fluidic pathway within a desalination unit,the control system may selectively direct the fouled fluidic pathway tobe cleaned (e.g., by selectively flowing a de-scaling compositionthrough the fouled fluidic pathway). In some cases, one or moredesalination units that do not contain a fouled fluidic pathway maycontinue operation while one or more desalination units that contain afouled fluidic pathway are cleaned.

In some instances, scale can form on one or more surfaces of adesalination unit during a desalination process. Generally, scaleformation involves the deposition of solid salts (“scale”) from a fluidstream onto a surface that is not transported along with the fluidstream. For example, the deposition of solid salts from a fluid streamflowing through a heat exchanger on a wall of the heat exchanger wouldbe considered scale formation. On the other hand, formation of solidsalts on suspended solids that are transported into and out of the heatexchanger during operation of the heat exchanger would not be consideredscale formation.

Scale formed within a desalination unit may be any type of scale. Insome embodiments, the scale formed within a desalination unit comprisesa salt comprising at least one of Mg²⁺, Ca²⁺, Sr²⁺, and/or Ba²⁺. Incertain embodiments, the scale that is formed within the desalinationunit comprises a salt comprising a carbonate anion (CO₃ ²⁻), bicarbonateanion (HCO₃ ⁻), sulfate anion (SO₄ ²⁻), bisulfate anion (HSO₄ ⁻),dissolved silica (e.g., SiO₂(OH)₂ ²⁻, SiO(OH)³⁻, (SiO₃ ²⁻)_(n), and thelike), and/or hydroxide ion (OH). In some embodiments, the scale that isformed in the desalination unit is a salt comprising at least one ofMg²⁺, Ca²⁺, Sr²⁺, and/or Ba²⁺, and at least one of carbonate anions (CO₃²⁻), bicarbonate anions (HCO₃ ⁻), sulfate anions (SO₄ ²⁻), bisulfateanions (HSO₄ ⁻), dissolved silica (e.g., SiO₂(OH)₂ ²⁻, SiO(OH)³⁻, (SiO₃²⁻)_(n). In certain embodiments, the scale that is formed in thedesalination unit comprises a salt comprising strontium (e.g., Sr²⁺),such as strontium sulfate. In some embodiments, the scale formed withina desalination unit is “hard scale,” which, as used herein, refers toprecipitated sulfates and precipitated divalent cations such as calcium,magnesium, barium, and strontium. In some embodiments, the scale formedwithin a desalination unit is “soft scale,” which, as used herein,refers to crystalline carbonate salts and/or hydroxide salts.

Scale may form on any surface of a desalination unit. Generally, anysurface of the desalination unit that contacts the salt-containing fluidstream during the desalination process is potentially susceptible toscale formation. In some cases, scale may be more likely to form onsurfaces of heat exchangers than on surfaces of other components of adesalination unit. For example, in certain instances, elevated surfacetemperatures and/or comparatively rough surfaces of heat exchangers maymake heat exchanger surfaces particularly vulnerable to scale formation.Since scale is often thermally insulating, the formation and build-up ofscale on heat exchanger surfaces can result in a substantiallydetrimental impact on the efficiency of the desalination unit relativeto the impact of scale formation on other surfaces, such as surfaceswithin the humidifier. Thus, reducing the amount of scale present on thesurfaces of the heat exchanger(s) of the desalination unit is generallydesirable.

Scale formation may be facilitated by a variety of factors, including,but not limited to, temperature variation, flow rate variation, surfaceroughness, and the presence of co-precipitates. Given the range offactors that may facilitate scale formation, scale may begin to form atdifferent times in different desalination units, even if thedesalination units are substantially identical in structure and areoperated under substantially identical conditions. Accordingly, it maybe challenging to determine when a particular desalination unit of amulti-unit desalination system should undergo a de-scaling process.However, within the context of this invention, certain detection andcontrol methods that may allow identification of desalination units inwhich scale has begun forming, such that one or more de-scalingcompositions may be flowed through those desalination units to at leastpartially remove scale, have been developed and are described below. Incertain embodiments, the temperature and/or flow rate of each heatingfluid stream flowing through the plurality of desalination units ismeasured, and an average temperature and/or flow rate of the heatingfluid streams flowing through the plurality of desalination units iscalculated. In certain cases, a higher than average temperature and/or alower than average flow rate in a particular desalination unit mayindicate that scale has begun forming in that particular desalinationunit, and a de-scaling composition is then selectively flowed through atleast a portion of that desalination unit.

In some embodiments, a method of removing scale comprises providing aplurality of desalination units. For example, FIG. 12 is a schematicdiagram of an exemplary desalination system 1200 comprising a pluralityof desalination units. As shown in FIG. 12, exemplary desalinationsystem 1200 comprises first desalination unit 1202A and seconddesalination unit 1202B. Although 2 exemplary desalination units areillustrated in FIG. 12, it should be understood that a desalinationsystem may comprise any number of additional desalination units. In someembodiments, the plurality of desalination units comprises at least 2desalination units, at least 3 desalination units, at least 4desalination units, at least 5 desalination units, at least 10desalination units, at least 20 desalination units, at least 50desalination units, or at least 100 desalination units. In someembodiments, the plurality of desalination units comprises between 2 and100 desalination units, between 3 and 100 desalination units, between 4and 100 desalination units, between 5 and 100 desalination units,between 10 and 100 desalination units, between 20 and 100 desalinationunits, or between 50 and 100 desalination units.

The desalination units of the plurality of desalination units mayindependently be any type of suitable desalination unit. Examples ofsuitable types of desalination units include, but are not limited to,HDH desalination units, mechanical vapor compression units, multi-effectdistillation units, multi-stage flash units, vacuum distillation units,and directional solvent extraction units. In some embodiments, two ormore (or all) of the plurality of desalination units are HDHdesalination units (e.g., desalination units comprising a humidifier anda dehumidifier). In certain cases, two or more (or all) of the HDHdesalination units are mobile HDH desalination units. In certainembodiments, the humidifier (e.g., bubble column humidifier) anddehumidifier (e.g., bubble column condenser) are housed within a singlevessel, forming a combined HDH apparatus (e.g., an integrated HDHdesalination unit). In certain cases, the vessel has a relatively lowheight and/or a relatively small footprint. In certain embodiments, thehumidifier (e.g., bubble column humidifier) is housed within a firstvessel and the dehumidifier (e.g., bubble column condenser) is housedwithin a second, separate vessel. In certain cases, the first vesseland/or second vessel have a relatively low height and/or a relativelysmall footprint.

In FIG. 12, first desalination unit 1202A comprises humidifier 1204A,and second desalination unit 1202B comprises humidifier 1204B. Thehumidifier of each HDH desalination unit of a desalination system mayindependently be any type of suitable humidifier. Non-limiting examplesof suitable humidifiers include bubble column humidifiers and packed bedhumidifiers.

In FIG. 12, first desalination unit 1202A further comprises dehumidifier1206A fluidically connected to humidifier 1204A (fluidic connection notshown in FIG. 12), and second desalination unit 1202B further comprisesdehumidifier 1206B fluidically connected to humidifier 1204B (fluidicconnection not shown in FIG. 12). The dehumidifier of each HDHdesalination unit may independently be any type of suitabledehumidifier. Non-limiting examples of suitable dehumidifiers includebubble column condensers, surface condensers, spray towers, and packedbed towers.

In some embodiments, the two or more HDH desalination units of theplurality of desalination units are heat exchanger-containingdesalination units, each heat exchanger-containing desalination unitfurther comprising a first heat exchanger. For example, in FIG. 12,first desalination unit 1202A further comprises first heat exchanger1208A, and second desalination unit 1202B further comprises first heatexchanger 1208B. In some embodiments, the first heat exchanger of adesalination unit comprises a first fluidic pathway having an inlet andan outlet and a second fluidic pathway having an inlet and an outlet,and the first heat exchanger is configured to transfer heat between afirst fluid stream flowing through the first fluidic pathway and asecond fluid stream flowing through the second fluidic pathway.

In certain embodiments, the first fluid stream flowing through the firstheat exchanger is a salt-containing water stream. In some cases, thesalt-containing water stream comprises seawater, brackish water,flowback water, water produced from an oil or gas extraction process,and/or wastewater. Non-limiting examples of wastewater include textilemill wastewater, leather tannery wastewater, paper mill wastewater,cooling tower blowdown water, flue gas desulfurization wastewater,landfill leachate water, and/or the effluent of a chemical process(e.g., the effluent of another desalination system and/or chemicalprocess).

In certain embodiments, the second fluid stream flowing through thefirst heat exchanger is a heating fluid stream. The heating fluid may beany fluid capable of absorbing and transferring heat. Examples ofsuitable heating fluids include, but are not limited to, water, air,saturated/superheated steam, synthetic organic-based non-aqueous fluids,glycol, brines, and/or mineral oils.

In some embodiments, the first heat exchanger of a heatexchanger-containing desalination unit is fluidically connected (e.g.,directly fluidically connected) to the humidifier of the heatexchanger-containing desalination unit. In certain embodiments, a liquidoutlet of the first heat exchanger (e.g., a liquid outlet of the firstfluidic pathway) is fluidically connected to a liquid inlet of thehumidifier (e.g., a main humidifier liquid inlet). In FIG. 12, forexample, liquid outlet 1248A of the first fluidic pathway of first heatexchanger 1208A of first desalination unit 1202A is directly fluidicallyconnected to main humidifier liquid inlet 1256A of humidifier 1204A offirst desalination unit 1202A. FIG. 12 also shows liquid outlet 1248B ofthe first fluidic pathway of first heat exchanger 1208B of seconddesalination unit 1202B as being directly fluidically connected to mainhumidifier liquid inlet 1256B of humidifier 1204B of second desalinationunit 1202B.

In some embodiments, the first heat exchanger of a heatexchanger-containing desalination unit is further fluidically connected(e.g., directly fluidically connected) to a source of a first fluidstream (e.g., a salt-containing water stream). The source of the firstfluid stream may be a common source for all the heatexchanger-containing desalination units of a system. In some cases, forexample, the first heat exchanger (e.g., the first fluidic pathway ofthe first heat exchanger) of each heat exchanger-containing desalinationunit is fluidically connected to a common salt-containing water source(e.g., a central feed tank). In FIG. 12, central feed tank 1218, whichis configured to receive influent liquid stream 1222, is fluidicallyconnected to first desalination unit 1202A and second desalination unit1202B. In particular, liquid inlet 1252A of the first fluidic pathway offirst heat exchanger 1208A of first desalination unit 1202A and liquidinlet 1252B of the first fluidic pathway of first heat exchanger 1208Bof second desalination unit 1202B are both fluidically connected tocentral feed tank 1218. In some cases, the presence of a central feedtank may allow the salinities of the salt-containing water streamsentering the heat exchanger-containing desalination units to besubstantially constant. Alternatively, each heat exchanger-containingdesalination unit may be fluidically connected to a differentsalt-containing water source. For example, each heatexchanger-containing desalination unit may comprise its own sump thatoperates as a feed tank for the desalination unit.

In some embodiments, the first heat exchanger of a heatexchanger-containing desalination unit is further fluidically connected(e.g., directly fluidically connected) to a source of a second fluidstream (e.g., a heating fluid stream). The source of the second fluidstream may be a common source for all the heat exchanger-containingdesalination units of a system. In some cases, for example, the firstheat exchanger (e.g., the second fluidic pathway of the first heatexchanger) of each heat exchanger-containing desalination units isfluidically connected to a common heating fluid source (e.g., a boiler).In FIG. 12, common heating fluid source 1220 is fluidically connected tofirst desalination unit 1202A and second desalination unit 1202B. Inparticular, liquid inlet 1254A of the second fluidic pathway of firstheat exchanger 1208A of first desalination unit 1208A and liquid inlet1254B of the second fluidic pathway of first heat exchanger 1208B ofsecond desalination unit 1208B are both fluidically connected to commonheating fluid source 1220. In some cases, the presence of a commonheating fluid source may allow the temperatures of the heating fluidstreams entering the heat exchanger-containing desalination units to besubstantially constant. Alternatively, each heat exchanger-containingdesalination unit may be fluidically connected to a different heatingfluid source. For example, each heat exchanger-containing desalinationunits may comprise or be fluidically connected to a different boiler.

In some embodiments, some or all of the heat exchanger-containingdesalination units further comprise at least a second heat exchangerfluidically connected to the first heat exchanger. For example, firstdesalination unit 1202A further comprises second heat exchanger 1210A.In some embodiments, the second heat exchanger of a desalination unitcomprises a first fluidic pathway having an inlet and an outlet and asecond fluidic pathway having an inlet and an outlet, and the secondheat exchanger is configured to transfer heat between a first fluidstream flowing through the first fluidic pathway and a second fluidstream flowing through the second fluidic pathway. In some cases, thesecond heat exchanger may be referred to as an “energy recovery heatexchanger.”

In some embodiments, the first fluid stream flowing through the secondheat exchanger is a salt-containing water stream entering thehumidifier. In some cases, the second heat exchanger (e.g., a liquidinlet of the first fluidic pathway of the second heat exchanger) isfluidically connected (e.g., directly fluidically connected) to asalt-containing water source (e.g., a central feed tank). In addition,the second heat exchanger may be fluidically connected (e.g., directlyfluidically connected) to the first heat exchanger and/or thehumidifier. For example, a liquid outlet of the second heat exchanger(e.g., a liquid outlet of the first fluidic pathway of the second heatexchanger) may be fluidically connected (e.g., directly fluidicallyconnected) to a liquid inlet of the first heat exchanger (e.g., a liquidinlet of the first fluidic pathway of the first heat exchanger) and/or aliquid inlet of the humidifier (e.g., a main humidifier liquid inlet).In FIG. 12, for example, second heat exchanger 1210A of firstdesalination unit 1202A is directly fluidically connected to first heatexchanger 1208A and central feed tank 1218, and second heat exchanger1210B of second desalination unit 1202B is directly fluidicallyconnected to first heat exchanger 1208B and central feed tank 1218. Inparticular, in first desalination unit 1202A, liquid inlet 1258A of thefirst fluidic pathway of second heat exchanger 1210A is fluidicallyconnected to central feed tank 1218, and liquid outlet 1260A of thefirst fluidic pathway of second heat exchanger 1210A is fluidicallyconnected to liquid inlet 1252A of the first fluidic pathway of firstheat exchanger 1208A. In second desalination unit 1202B, liquid inlet1258B of the first fluidic pathway of second heat exchanger 1210B isfluidically connected to central feed tank 1218, and liquid outlet 1260Bof the first fluidic pathway of second heat exchanger 1210B isfluidically connected to liquid inlet 1252B of the first fluidic pathwayof first heat exchanger 1208B.

In some embodiments, the second fluid stream flowing through the secondheat exchanger is a water stream exiting the dehumidifier. Accordingly,in some cases, the second heat exchanger is fluidically connected (e.g.,directly fluidically connected) to the dehumidifier. For example, aliquid inlet (e.g., a liquid inlet of the second fluidic pathway) of thesecond heat exchanger may be fluidically connected (e.g., directlyfluidically connected) to a liquid outlet of the dehumidifier (e.g., amain dehumidifier liquid outlet). In some cases, a liquid outlet (e.g.,a liquid outlet of the second fluidic pathway) of the second heatexchanger may be fluidically connected (e.g., directly fluidicallyconnected) to a liquid inlet of the dehumidifier (e.g., a maindehumidifier liquid inlet). In FIG. 12, for example, second heatexchanger 1210A of first desalination unit 1202A is fluidicallyconnected to dehumidifier 1206A, and second heat exchanger 1210B ofsecond desalination unit 1202B is fluidically connected to dehumidifier1206B. In particular, in first desalination unit 1202A, liquid inlet1262A of the second fluidic pathway of second heat exchanger 1210A isfluidically connected to main dehumidifier liquid outlet 1266A ofdehumidifier 1206A, and liquid outlet 1264A of the second fluidicpathway of second heat exchanger 1210A is fluidically connected to maindehumidifier liquid inlet 1268A of dehumidifier 1206A. In seconddesalination unit 1202B, liquid inlet 1262B of the second fluidicpathway of second heat exchanger 1210B is fluidically connected to maindehumidifier liquid outlet 1266B of dehumidifier 1206B, and liquidoutlet 1264B of the second fluidic pathway of second heat exchanger1210B is fluidically connected to main dehumidifier liquid inlet 1268Bof dehumidifier 1206B.

The first heat exchanger and second heat exchanger of a heatexchanger-containing desalination unit may be any type of heat exchangerknown in the art. Examples of suitable heat exchangers include, but arenot limited to, plate-and-frame heat exchangers, shell-and-tube heatexchangers, tube-and-tube heat exchangers, plate heat exchangers,plate-and-shell heat exchangers, spiral heat exchangers, and the like.In a particular embodiment, the first heat exchanger and/or second heatexchanger are plate-and-frame heat exchangers. In certain embodiments,the first heat exchanger and/or second heat exchanger are configuredsuch that a first fluid stream and a second fluid stream flow throughthe first heat exchanger and/or second heat exchanger. In some cases,the first fluid stream and the second fluid stream may flow insubstantially the same direction (e.g., parallel flow), substantiallyopposite directions (e.g., counter flow), or substantially perpendiculardirections (e.g., cross flow). In some cases, more than two fluidstreams may flow through the first heat exchanger and/or second heatexchanger. In an exemplary embodiment, the first heat exchanger and/orsecond heat exchanger are counter-flow plate-and-frame heat exchangers.In some cases, a counter-flow plate-and-frame heat exchanger mayadvantageously result in a small temperature difference between twofluid streams flowing through the heat exchanger. A non-limiting exampleof a suitable commercially available heat exchanger is Plate ConceptsModu-Flex Plate & Frame Product # MFL041D1PA150-115.

In some embodiments, the first fluid stream and/or second fluid streamflowing through the first heat exchanger and/or the second heatexchanger of a heat exchanger-containing desalination unit comprise aliquid. In some embodiments, the first heat exchanger and/or second heatexchanger are liquid-to-liquid heat exchangers (e.g., the first fluidstream and the second fluid stream comprise a liquid). In someembodiments, the first fluid stream and/or second fluid stream flowingthrough the first heat exchanger and/or the second heat exchangercomprise a gas (e.g., air or saturated/superheated steam). In certaincases, the first fluid stream and/or second fluid stream do not undergoa phase change (e.g., liquid to gas or vice versa) within the first heatexchanger and/or the second heat exchanger. In some cases, more than twofluid streams flow through the first heat exchanger and/or the secondheat exchanger.

In some embodiments, a relatively large amount of heat may betransferred between the first fluid stream and the second fluid streamflowing through the first heat exchanger or the second heat exchanger ofa heat exchanger-containing desalination unit and/or a relatively largetemperature difference driving force may exist or be established betweenthe first fluid stream and the second fluid stream flowing through thefirst heat exchanger or the second heat exchanger. For example, thedifference between the temperature of a fluid stream entering the firstor second heat exchanger and the fluid stream exiting the first orsecond heat exchanger may be at least about 5° C., at least about 10°C., at least about 15° C., at least about 20° C., at least about 30° C.,at least about 40° C., at least about 50° C., at least about 60° C., atleast about 70° C., at least about 80° C., or at least about 90° C. Insome embodiments, the difference between the temperature of a fluidstream entering the first or second heat exchanger and the temperatureof the fluid stream exiting the first or second heat exchanger is in therange of about 5° C. to about 20° C., about 5° C. to about 30° C., about5° C. to about 50° C., about 5° C. to about 60° C., about 5° C. to about90° C., about 10° C. to about 30° C., about 10° C. to about 60° C.,about 10° C. to about 90° C., about 20° C. to about 60° C., about 20° C.to about 90° C., about 30° C. to about 60° C., about 30° C. to about 90°C., about 50° C. to about 90° C., about 60° C. to about 90° C., or about70° C. to about 90° C.

In some embodiments, a desalination system comprising a plurality ofdesalination units further comprises a control system in electroniccommunication with the desalination units. For example, in certainembodiments, some or all of the first heat exchangers of thedesalination units may be coupled to a controller configured to receivean input signal from at least one input device and to deliver an outputsignal, in response to the input signal, to at least one output device.According to some embodiments, the controller comprises a PID controllerthat operates according to a proportional-integral-derivative controlloop. However, other control loop feedback mechanisms may be used, aswould be understood by a person of ordinary skill in the art.

In certain embodiments, the controller (e.g., a PID controller) iscoupled (e.g., electronically coupled) to at least one input deviceand/or at least one output device. In some cases, the at least one inputdevice comprises a sensor configured to monitor a parameter (e.g.,temperature, flow rate) associated with a component (e.g., a first heatexchanger) of a desalination unit. In some cases, the at least one inputdevice is positioned within or in proximity to the component (e.g.,first heat exchanger) of the desalination unit. The at least one inputdevice may be configured to send an input signal (e.g., corresponding toa measurement taken by the at least one input device) to the controller,and the controller may be configured to receive the input signal. Insome cases, the at least one input device regularly or continuouslytransmits an input signal to the controller. Non-limiting examples ofsuitable input devices include a dial thermometer, a thermocouple, apaddle wheel flow meter, a rotameter, an ultrasonic flow meter, and amass flow meter.

In some embodiments, the controller, in response to an input signalreceived from the at least one input device, delivers an output signalto at least one output device (e.g., to direct operation of the at leastone output device). In some cases, the at least one output devicecomprises a device that affects a parameter (e.g., flow rate) associatedwith a component (e.g., a first heat exchanger) of a desalination unit.In some embodiments, the at least one output device is in fluidiccommunication with the component (e.g., first heat exchanger) of thedesalination unit. In some embodiments, the at least one output deviceis positioned within or in proximity to the component (e.g., first heatexchanger) of the desalination unit. In certain embodiments, the atleast one output device can direct flow of a fluid stream (e.g., a firstliquid stream, a second liquid stream) through the component (e.g.,first heat exchanger) of the desalination unit. Non-limiting examples ofsuitable output devices include a pump, a valve, and/or a mass flowcontroller.

In FIG. 12, desalination system 1200 comprises control system 1244. Asshown in FIG. 12, control system 1244 is electronically connected tofirst heat exchanger 1208A of first desalination unit 1202A viaelectronic connection 1246A, and control system 1244 is electronicallyconnected to first heat exchanger 1208B of second desalination unit1202B via electronic connection 1246B,

In some embodiments, the method of removing scale comprises flowing afirst fluid stream (e.g., a salt-containing water stream) through afirst fluidic pathway of the first heat exchanger of each heatexchanger-containing desalination unit. In some cases, the methodcomprises flowing a salt-containing water stream from a commonsalt-containing water source (e.g., a central feed tank) to the firstheat exchanger of each heat exchanger-containing desalination unit. Forexample, referring to FIG. 12, the method may comprise flowing asalt-containing water stream from central feed tank 1218 to liquid inlet1252A of the first fluidic pathway of first heat exchanger 1208A offirst desalination unit 1202A and to liquid inlet 1252B of the firstfluidic pathway of first heat exchanger 1208B of second desalinationunit 1202B.

In some embodiments, the method of removing scale comprises flowing asecond fluid stream (e.g., a heating fluid stream) through a secondfluidic pathway of the first heat exchanger of each heatexchanger-containing desalination unit. In some cases, the methodcomprises flowing a heating fluid stream from a common heating fluidsource (e.g., a boiler) to the first heat exchanger of each heatexchanger-containing desalination unit. For example, referring to FIG.12, the method may comprise flowing heating fluid stream 1232A fromcommon heating fluid source 1220 to liquid inlet 1254A of the secondfluidic pathway of first heat exchanger 1208A of first desalination unit1202A and flowing heating fluid stream 1232B from common heating fluidsource 1220 to liquid inlet 1254B of the second fluidic pathway of firstheat exchanger 1208B of second desalination unit 1202B. In first heatexchanger 1208A of first desalination unit 1202A, heat may betransferred from heating fluid stream 1232A to salt-containing waterstream 1226A (which may have been heated in second heat exchanger1210A), thereby producing heated salt-containing water stream 1228A andcooled heating fluid stream 1234A. In first heat exchanger 1208B ofsecond desalination unit 1202B, heat may be transferred from heatingfluid stream 1232B to salt-containing water stream 1226B (which may havebeen heated in second heat exchanger 1210B), thereby producing heatedsalt-containing water stream 1228B and cooled heating fluid stream1234B.

According to some embodiments, the method further comprises measuring afirst temperature of at least two, some, or each of all the second fluidstreams of the heat exchangers (e.g., heating fluid streams). In someembodiments, the first temperature of a second fluid stream (e.g.,heating fluid stream) is measured downstream of the first heatexchanger. In certain cases, for example, the first temperature of asecond fluid stream flowing through a heat exchanger-containingdesalination unit is measured at a liquid outlet of the second fluidicpathway of the first heat exchanger of the heat exchanger-containingdesalination unit. Referring to FIG. 12, the first temperature ofheating fluid stream 1234A may be measured at liquid outlet 1250A offirst heat exchanger 1208A of first desalination unit 1202A, and thefirst temperature of heating fluid stream 1234B may be measured atliquid outlet 1250B of first heat exchanger 1208A of second desalinationunit 1202B. However, the first temperature of the second fluid streammay be measured at other locations downstream of the first heatexchanger.

In some cases, the first temperature of the second fluid stream (e.g.,heating fluid stream) may be measured using an input device configuredto send a signal to a control system. The input device may be anysuitable temperature measurement device known in the art. Non-limitingexamples of suitable temperature measurement devices include dialthermometers and thermocouples. In some cases, the temperature of afluid stream (e.g., the second fluid stream) may be relatively easy tomonitor because the temperature displayed by a temperature measurementdevice (e.g., a dial thermometer, a thermocouple) may change relativelyslowly. In certain cases, temperature measurements may be relativelyresistant to minor fluctuations, and, accordingly, may be more reliablethan other types of measurements.

In some cases, the method further comprises determining an average firsttemperature of at least two, some, or all the first temperatures of thesecond fluid streams measured in the measuring step. As used herein, theaverage first temperature of the second fluid streams refers to thenumber average of the first temperatures of the second fluid streams(e.g., the sum of the first temperatures of all the second fluid streamsdivided by the number of second fluid streams). In some embodiments, thestep of determining the average first temperature is performed by thecontroller of a control system.

In some cases, the method further comprises identifying at least onefouled first fluidic pathway. In certain cases, scale formation withinthe first heat exchanger (e.g., the first fluidic pathway of the firstheat exchanger) of a desalination unit may cause the first temperatureof a second fluid stream (e.g., heating fluid stream) exiting the firstheat exchanger to increase (e.g., due to the thermally insulatingeffects of scale). For example, the presence of scale within the firstheat exchanger may result in less heat per volume of the second fluidstream (e.g., heating fluid stream) being transferred to the first fluidstream (e.g., salt-containing water stream) flowing through the firstheat exchanger, thereby causing the temperature of the second fluidstream exiting the first heat exchanger to be greater than thetemperature of a second fluid stream flowing through a first heatexchanger without scale. Accordingly, in some cases, a relatively hightemperature of a second fluid stream exiting a first heat exchanger maybe used to identify a fouled first fluidic pathway of a first heatexchanger. In some embodiments, a fouled first fluidic pathway of afirst heat exchanger is characterized by a first temperature of a secondfluid stream that differs from (e.g., is greater than) the average firsttemperature of the second fluid streams by at least about 5%, at leastabout 10%, at least about 20%, at least about 30%, at least about 40%,at least about 50%, at least about 75%, at least about 100%, at leastabout 125%, or at least about 150% on the Kelvin scale. In certainembodiments, a fouled first fluidic pathway of a first heat exchanger ischaracterized by a first temperature of a second fluid stream thatdiffers from (e.g., is greater than) the average first temperature ofthe second fluid streams by an amount in the range of about 5% to about150%, about 10% to about 150%, about 20% to about 150%, about 30% toabout 150%, about 40% to about 150%, about 50% to about 150%, about 75%to about 150%, or about 100% to about 150% on the Kelvin scale. Forexample, this can be determined by taking the first temperature of eachsecond fluid stream, converting to Kelvin if necessary, calculating theaverage first temperature of the second fluid streams in Kelvin, andcalculating the percent difference between the first temperature inKelvin of a second fluid stream and the average first temperature inKelvin of the second fluid streams.

According to some embodiments, the method further comprises measuring afirst temperature of each first fluid stream (e.g., salt-containingwater stream). In some embodiments, the first temperature of a firstfluid stream (e.g., salt-containing water stream) is measured downstreamof the first heat exchanger. In certain cases, for example, the firsttemperature of a first fluid stream flowing through a heatexchanger-containing desalination unit is measured at a liquid outlet ofthe first fluidic pathway of the first heat exchanger. Referring to FIG.12, the first temperature of heated salt-containing water stream 1228Amay be measured at liquid outlet 1248A of the first fluidic pathway offirst heat exchanger 1208A of first desalination unit 1202A, and thefirst temperature of heated salt-containing water stream 1228B may bemeasured at liquid outlet 1248B of the first fluidic pathway of firstheat exchanger 1208B of second desalination unit 1202B. However, thefirst temperature of the first fluid stream may be measured at otherlocations downstream of the first heat exchanger. For example, incertain embodiments, the first temperature of a first fluid stream(e.g., salt-containing water stream) may be measured at a liquid inletof the humidifier (e.g., liquid inlet 1256A or 1256B in FIG. 12) and/orat a point along a conduit between the first heat exchanger and thehumidifier.

In some cases, the first temperature of the first fluid stream (e.g.,salt-containing water stream) may be measured using an input deviceconfigured to send a signal to a control system. The input device may beany suitable temperature measurement device known in the art.Non-limiting examples of suitable temperature measurement devicesinclude dial thermometers and thermocouples.

In some cases, the method further comprises determining an average firsttemperature of all the first temperatures of the first fluid streams. Asused herein, the average first temperature of the first fluid streamsrefers to the number average of the first temperatures of the firstfluid streams (e.g., the sum of the first temperatures of all the firstfluid streams divided by the number of first fluid streams). In someembodiments, the step of determining the average first temperature isperformed by the controller of a control system.

In some cases, the method further comprises identifying at least onefouled first fluidic pathway. In some cases, scale formation within thefirst heat exchanger of a desalination unit may cause the firsttemperature of a first fluid stream (e.g., a salt-containing waterstream) exiting the first heat exchanger of the desalination unit todecrease (e.g., due to the thermally insulating effects of scale). Forexample, the presence of scale within the first heat exchanger mayresult in less heat per volume of the second fluid stream (e.g., heatingfluid stream) being transferred to the first fluid stream (e.g.,salt-containing water stream) flowing through the first heat exchanger,thereby causing the temperature of the first fluid stream exiting thefirst heat exchanger to be less than the temperature of a first fluidstream flowing through a first heat exchanger without scale.Accordingly, in some cases, a relatively low first temperature of afirst fluid stream exiting a first heat exchanger may be used toidentify a fouled first fluidic pathway. In some embodiments, a fouledfirst fluidic pathway of a first heat exchanger may be characterized bya first temperature of a first fluid stream that differs from (e.g., isless than) the average first temperature of the first fluid streams byat least about 5%, at least about 10%, at least about 20%, at leastabout 30%, at least about 40%, at least about 50%, at least about 75%,at least about 100%, at least about 125%, or at least about 150% on theKelvin scale. In certain embodiments, a fouled first fluidic pathway ofa first heat exchanger may be characterized by a first temperature of afirst fluid stream that differs from (e.g., is less than) the averagefirst temperature of the first fluid streams by an amount in the rangeof about 5% to about 150%, about 10% to about 150%, about 20% to about150%, about 30% to about 150%, about 40% to about 150%, about 50% toabout 150%, about 75% to about 150%, or about 100% to about 150% on theKelvin scale.

According to some embodiments, the method further comprises increasing aflow rate of a second fluid stream (e.g., a heating fluid stream)flowing through a first heat exchanger of a desalination unit if thefirst temperature of a first fluid stream (e.g., a salt-containing waterstream) flowing through the desalination unit falls below a thresholdtemperature. For example, increasing the flow rate of the second fluidstream may increase the amount of heat transferred to the first fluidstream over a particular time period, thereby compensating for thepresence of scale and increasing the first temperature of the firstfluid stream such that it is at or above the threshold temperature.

In certain embodiments, the step of increasing the flow rate of a secondfluid stream (e.g., a heating fluid stream) is performed by the controlsystem. In some cases, the control system is configured to maintain arelatively constant temperature of the first fluid stream (e.g.,salt-containing water stream) exiting the first heat exchanger. Incertain cases, if the first temperature of the first fluid stream fallsbelow a threshold temperature (e.g., a temperature programmed into thecontrol system), the flow rate of the second fluid stream (e.g., heatingfluid stream) may be increased to transfer additional heat to the firstfluid stream and thereby increase the temperature of the first fluidstream exiting the first heat exchanger.

According to some embodiments, the method further, or alternatively,comprises measuring a first flow rate of at least two, some, or each ofall the second fluid streams (e.g., heating fluid streams) of the heatexchangers. In some embodiments, the first flow rate of a second fluidstream (e.g., heating fluid stream) is measured downstream of the firstheat exchanger. In certain cases, for example, the first flow rate of asecond fluid stream (e.g., heating fluid stream) flowing through a heatexchanger-containing desalination unit is measured at a liquid outlet ofthe second fluidic pathway of the first heat exchanger of thedesalination unit. Referring to FIG. 12, the first flow rate of heatingfluid stream 1234A may be measured at liquid outlet 1250A of first heatexchanger 1208A of first desalination unit 1202A, and the first flowrate of heating fluid stream 1234B may be measured at liquid outlet1250B of first heat exchanger 1208A of second desalination unit 1202B.However, the first flow rate may be measured at other locationsdownstream of the first heat exchanger.

In some cases, the first flow rate of the second fluid stream (e.g.,heating fluid stream) may be measured using an input device configuredto send a signal to a control system. The input device may be anysuitable flow rate measurement device known in the art. Non-limitingexamples of suitable flow rate measurement devices include paddle wheelflow meters, rotameters, ultrasonic flow meters, and mass flow meters.In some embodiments, the first flow rate refers to a mass flow rate. Insome embodiments, the first flow rate refers to a volumetric flow rate.

In some embodiments, the method further comprises determining an averagefirst flow rate of at least two, some, or all the first flow rates ofthe second fluid streams. As used herein, the average first flow rate ofthe second fluid streams refers to the number average of the first flowrates of the second fluid streams (e.g., the sum of the first flow ratesof all the second fluid streams divided by the number of second fluidstreams). In some embodiments, the step of determining the average firstflow rate is performed by the controller of a control system.

In some cases, the method further comprises identifying at least onefouled first fluidic pathway. In some cases, scale formation within thefirst heat exchanger of a desalination unit may cause the first flowrate of a second fluid stream (e.g., heating fluid stream) exiting thefirst heat exchanger of the desalination unit to increase. For example,the presence of scale within the first heat exchanger may result in lessheat per volume of the second fluid stream (e.g., heating fluid stream)being transferred to the first fluid stream (e.g., salt-containing waterstream) flowing through the first heat exchanger, thereby causing thefirst temperature of the first fluid stream to be relatively low. Asnoted above, in certain embodiments, if the first temperature of thefirst fluid stream falls below a threshold temperature, the flow rate ofthe second fluid stream may be increased to compensate. Accordingly, arelatively high first flow rate of a second fluid stream exiting a firstheat exchanger may indicate the presence of scale within the first heatexchanger. Therefore, in some embodiments, a fouled first fluidicpathway may be characterized by a flow rate of a second fluid streamthat differs from (e.g., is greater than) the average first flow rate ofthe second fluid streams by at least about 5%, at least about 10%, atleast about 20%, at least about 30%, at least about 40%, at least about50%, at least about 75%, at least about 100%, at least about 125%, or atleast about 150%. In certain embodiments, a fouled first fluidic pathwaymay be characterized by a flow rate of a second fluid stream thatdiffers from (e.g., is greater than) the average first flow rate of thesecond fluid streams by an amount in the range of about 5% to about150%, about 10% to about 150%, about 20% to about 150%, about 30% toabout 150%, about 40% to about 150%, about 50% to about 150%, about 75%to about 150%, or about 100% to about 150%.

According to some embodiments, the method further comprises measuring asecond temperature of at least two, some, or each of all the secondfluid streams (e.g., heating fluid streams) flowing through the heatexchanger-containing desalination units. In some embodiments, the secondtemperature of a second fluid stream (e.g., heating fluid stream)flowing through a heat exchanger-containing desalination unit ismeasured upstream of the first heat exchanger. In certain cases, forexample, the second temperature of a second fluid stream (e.g., heatingfluid stream) is measured at a liquid inlet of the second fluidicpathway of the first heat exchanger. Referring to FIG. 12, the secondtemperature of heating fluid stream 1232A may be measured at liquidinlet 1254A of the second fluidic pathway of first heat exchanger 1208Aof first desalination unit 1202A, and the second temperature of heatingfluid stream 1232B may be measured at liquid inlet 1254B of first heatexchanger 1208B of second desalination unit 1202B. However, the secondtemperature of the second fluid stream may be measured at otherlocations upstream of the first heat exchanger.

In some cases, the second temperature of the second fluid stream (e.g.,heating fluid stream) may be measured using an input device configuredto send a signal to a control system. The input device may be anysuitable temperature measurement device known in the art. Non-limitingexamples of suitable temperature measurement devices include dialthermometers and thermocouples.

In some embodiments, the method further comprises measuring anddetermining a relative standard deviation of at least two, some, or allthe second temperatures of the second fluid streams (e.g., heating fluidstreams). A standard deviation of the second temperatures of the secondfluid streams (e.g., heating fluid streams) can be determined accordingto Equation (1):

$\begin{matrix}{\sigma = \sqrt{\frac{1}{N}{\sum\limits_{i = 1}^{N}\; \left( {x_{i} - \overset{\_}{x}} \right)^{2}}}} & (1)\end{matrix}$

where N is the number of measured temperatures of the second fluidstreams, x is the mean second temperature, and x_(i) is the secondtemperature of the i^(th) second fluid stream. In certain cases, arelative standard deviation of the second temperatures of the secondfluid streams can be determined according to Equation (2):

$\begin{matrix}{{\% \mspace{14mu} {RSD}} = {\frac{\sigma}{\overset{\_}{x}} \times 100}} & (2)\end{matrix}$

where σ is the standard deviation of the second temperatures of thesecond fluid streams (as determined according to Equation (1)) and x isthe mean second temperature. In some embodiments, the relative standarddeviation of the second temperatures of the second fluid streams (e.g.,heating fluid streams) flowing through the heat exchanger-containingdesalination units is controlled and maintained (e.g. through the abovedescribed methods of fouling detection and descaling methods describedin greater detail below) to be about 50% or less, about 40% or less,about 30% or less, about 20% or less, about 10% or less, about 5% orless, or about 1% or less. In some embodiments, the relative standarddeviation of the second temperatures of the second fluid streams (e.g.,heating fluid streams) is in a range between about 1% to about 50%,about 1% to about 40%, about 1% to about 30%, about 1% to about 20%,about 1% to about 10%, or about 1% to about 5%. In certain embodiments,the second temperatures of the second fluid streams (e.g., heating fluidstreams) may be substantially similar because a common source of thesecond fluid streams (e.g., a boiler) supplies a second fluid stream toeach heat exchanger-containing desalination unit. In certainembodiments, the step of measuring and determining the relative standarddeviation is performed by the controller of a control system.

According to some embodiments, the method further comprises measuring asecond temperature of at least two, some or each of all first fluidstreams (e.g., salt-containing water streams) flowing through the heatexchanger-containing desalination units. In some embodiments, the secondtemperature of a first fluid stream (e.g., salt-containing water stream)flowing through a heat exchanger-containing desalination unit ismeasured upstream of the first heat exchanger. In certain cases, forexample, the second temperature of a first fluid stream (e.g.,salt-containing water stream) is measured at a liquid inlet of the firstfluidic pathway of the first heat exchanger. Referring to FIG. 12, thesecond temperature of salt-containing water stream 1226A may be measuredat liquid inlet 1252A of the first fluidic pathway of first heatexchanger 1208A of first desalination unit 1202A, and the secondtemperature of salt-containing water stream 1226B may be measured atliquid inlet 1252B of the first fluidic pathway of first heat exchanger1208B of second desalination unit 1202B.

In some cases, the second temperature of the first fluid stream (e.g.,salt-containing water stream) may be measured using an input deviceconfigured to send a signal to a control system. The input device may beany suitable temperature measurement device known in the art.Non-limiting examples of suitable temperature measurement devicesinclude dial thermometers and thermocouples.

In some embodiments, the second temperatures of the first fluid streamsentering the heat exchanger-containing desalination units arecontrolled/maintained to be substantially constant. In some embodiments,for example, the relative standard deviation of the second temperaturesof the first fluid streams (e.g., salt-containing water streams) flowingthrough the heat exchanger-containing desalination units is less thanabout 50%, less than about 40%, less than about 30%, less than about20%, less than about 10%, less than about 5%, or less than about 1%. Insome embodiments, the relative standard deviation of the secondtemperatures of the first fluid streams (e.g., salt-containing waterstreams) is in the range of about 1% to about 50%, about 1% to about40%, about 1% to about 30%, about 1% to about 20%, about 1% to about10%, or about 1% to about 5%.

In some embodiments, the method further comprises selectively flowing ade-scaling composition through only the at least one first fluidicpathway(s) determined, e.g., by the fouling detection methods describedabove, to be fouled to an extent warranting regeneration (e.g.,cleaning). In some cases, a de-scaling composition may be flowed througha fouled first fluidic pathway of a first heat exchanger of adesalination unit after a desalination process has been performed withinthe desalination unit.

A general summary of the operation of an exemplary desalination system,such as the one illustrated in FIG. 12, follows. In operation, asalt-containing water stream 1222 may enter desalination system 1200through central feed tank 1218. From central feed tank 1218, a firstsalt-containing water stream 1224A may be directed to flow to secondheat exchanger 1210A of first desalination unit 1202A, and a secondsalt-containing water stream 1224B may be directed to flow to secondheat exchanger 1210B of second desalination unit 1202B. In second heatexchanger 1210A of first desalination unit 1202A, heat may betransferred from water stream 1236A exiting dehumidifier 1206A to firstsalt-containing water stream 1224A to produce heated salt-containingwater stream 1226A. Similarly, in second heat exchanger 1210B of seconddesalination unit 1202B, heat may be transferred from water stream 1236Bexiting dehumidifier 1206B to second salt-containing water stream 1224Bto produce heated salt-containing water stream 1226B. Heatedsalt-containing water streams 1226A and 1226B may then directed to flowto first heat exchangers 1208A and 1208B, respectively. At the sametime, first heating fluid stream 1232A and second heating fluid stream1232B may be directed to flow from common heating fluid source 1220 tofirst heat exchangers 1208A and 1208B, respectively. In first heatexchanger 1208A of first desalination unit 1202A, heated salt-containingwater stream 1226A may flow in a first direction through a first fluidicpathway of first heat exchanger 1208A, and first heating fluid stream1232A may flow in a second, substantially opposite direction through asecond fluidic pathway of first heat exchanger 1208A. As the two fluidstreams flow through first heat exchanger 1208A, heat may be transferredfrom first heating fluid stream 1232A to heated salt-containing waterstream 1226A to produce further heated salt-containing water stream1228A. Similarly, in first heat exchanger 1208B of second desalinationunit 1202B, heated salt-containing water stream 1226B may flow in afirst direction through a first fluidic pathway of first heat exchanger1208B, and second heating fluid stream 1232B may flow in a second,substantially opposite direction through a second fluidic pathway offirst heat exchanger 1208B. As the two fluid streams flow through firstheat exchanger 1208B, heat may be transferred from second heating fluidstream 1232B to heated salt-containing water stream 1226B to producefurther heated salt-containing water stream 1228B.

According to some embodiments, a first temperature of each of streams1228A and 1228B is measured. In some cases, for example, the firsttemperatures of streams 1228A and 1228B are measured at liquid outlets(e.g., liquid outlets of the first fluidic pathways) of first heatexchangers 1208A and 1208B. In certain embodiments, if the firsttemperature of stream 1228A or 1228B is below a certain threshold, anautomated feedback control system in electronic communication with firstdesalination unit 1202A and second desalination unit 1202B increases theflow rate of heating fluid streams 1232A or 1232B to increase the firsttemperature of stream 1228A or 1228B.

In some embodiments, a first temperature of each of heating fluidstreams 1234A and 1234B is measured. In some cases, for example, thefirst temperatures of heating fluid streams 1234A and 1234B are measuredat liquid outlets (e.g., liquid outlets of the second fluidic pathways)of first heat exchangers 1208A or 1208B. In certain embodiments, anaverage first temperature of the heating fluid streams is determined. Incertain cases, if the first temperature of heating fluid stream 1234A or1234B differs from (e.g., is greater than) the average first temperatureby a certain amount (e.g., at least about 10% on the Kelvin scale), thefirst fluidic pathway of the corresponding first heat exchanger isidentified as being fouled. In some cases, a de-scaling composition isselectively flowed through the fouled first fluidic pathway.

In some embodiments, a first flow rate of each of heating fluid streams1234A and 1234B is measured. In some cases, for example, the first flowrates of heating fluid streams 1234A and 1234B are measured at liquidoutlets (e.g., liquid outlets of the second fluidic pathways) of firstheat exchangers 1208A or 1208B. In certain embodiments, an average firstflow rate of the heating fluid streams is determined. In certain cases,if the first flow rate of heating fluid stream 1234A or 1234B differsfrom (e.g., is greater than) the average first flow rate by a certainamount (e.g., at least about 10%), the first fluidic pathway of thecorresponding first heat exchanger is identified as being fouled. Insome cases, a de-scaling composition is selectively flowed through thefouled first fluidic pathway.

According to some embodiments, the de-scaling composition is a liquidcomposition (e.g., an aqueous composition, a non-aqueous composition)comprising a multidentate ligand. In some cases, the de-scalingcomposition is directed to flow from a source of the de-scalingcomposition through at least one fouled first fluidic pathway (e.g., afirst fluidic pathway of at least one first heat exchanger). In somesuch embodiments, scale on a surface of the first heat exchanger can beat least partially removed by exposing the scale to the de-scalingcomposition comprising the at least one multidentate ligand. In certainembodiments, the multidentate ligand and a cationic species within thescale on the solid surface form a coordination complex that issubstantially soluble in the de-scaling composition. Without wishing tobe bound by any particular theory, it is believed that the multidentateligands can interact with ions already bonded in crystalline structuresof the scale, and that this interaction can force the metal cation outof its existing structure and into a central position within thecoordination complex, causing the scale to dissolve. After themultidentate ligand forms the coordination complex with the cationicspecies, the coordination complex can be dissolved in the de-scalingcomposition, and the scale can be removed from the solid surface of theheat exchanger. As one particular example, the strontium cation instrontium sulfate scale can be chelated using a multidentate ligand suchas diethylenetriaminepentaacetic acid (DTPA). The chelated ionsgenerally have a high solubility in water, and thus, will generallydissolve in an aqueous de-scaling composition. After dissolving in thede-scaling composition, the dissolved complexes can be transported awayby purging the de-scaling composition from the heat exchanger.

It should be understood that the use of the phrases “de-scaling” and“de-scaling composition” are not meant to imply that complete removal ofall scale from the surface(s) of the heat exchanger(s) is necessarilyachieved (although, in some embodiments, complete or substantiallycomplete removal of scale from the heat exchanger(s) may be achieved).In some cases, the de-scaling composition can be used to perform ade-scaling operation such that only a portion of the scale is removedfrom the surface(s) of the heat exchanger(s).

Any multidentate ligand that can form a complex with one or more ions ofa scale-forming salt can potentially be used in the de-scalingcomposition used to remove scale from the heat exchanger(s). The term“multidentate ligand,” as used herein, refers to a ligand that iscapable of forming a coordination complex with a central ion such thatmultiple parts of the ligand molecule interact with the central ion ofthe coordination complex. Those of ordinary skill in the art arefamiliar with the concept of multidenticity in the context of ligands.Multidentate ligands are sometimes also referred to by those of ordinaryskill in the art as multivalent ligands. In some embodiments, themultidentate ligand can comprise a bidentate ligand (i.e., a ligand withtwo parts that each interact with the central ion in a coordinationcomplex), a tridentate ligand (i.e., a ligand with three parts that eachinteract with the central ion in a coordination complex), a tetradentateligand (i.e., a ligand with four parts that each interact with thecentral ion in a coordination complex), a pentadentate ligand (i.e., aligand with five parts that each interact with the central ion in acoordination complex), a hexadentate ligand (i.e., a ligand with sixparts that each interact with the central ion in a coordinationcomplex), a heptadentate ligand (i.e., a ligand with seven parts thateach interact with the central ion in a coordination complex), and/or anoctadentate ligand (i.e., a ligand with eight parts that each interactwith the central ion in a coordination complex). Examples ofmultidentate ligands that can be used include, but are not limited to,triphosphate; nitrilotriacetic acid (NTA); inosine triphosphate;3,4-dihydroxybenzoic acid; uridine triphosphate; ATP; citric acid;oxalic acid; ADP; kojic acid; trimetaphosphate; maleic acid; globulin;casein; albumin; adipic acid; fumaric acid; malic acid; (+)-tartaricacid; glutamic acid; citraconic acid; itaconic acid; succinic acid;aspartic acid; glutaric acid; ethylenediaminetetraacetic acid (EDTA);and diethylenetriaminepentaacetic acid (DTPA).

In certain embodiments, the de-scaling composition used to remove scalefrom the heat exchanger(s) comprises diethylenetriaminepentaacetic acid(DTPA). DTPA can be a strong chelant and has been observed to formcoordinated complexes with strengths up to 100 times greater than thestrengths of those formed using EDTA. Without wishing to be bound by anyparticular theory, it is believed that the strength of DTPA as achelating agent may be due to its unusually high denticity. For example,at high pH values, DTPA can become a penta-anion, DTPA⁵⁻, and it isbelieved that each of the DTPA anion's three nitrogen centers and fiveCOO⁻ groups can act as a center for coordination, making DTPA anoctadentate ligand.

In some embodiments, the de-scaling composition contains multidentateligand(s) in an amount of at least about 10 wt %, at least about 20 wt%, at least about 30 wt %, at least about 40 wt %, at least about 45 wt%, at least about 50 wt %, or more. In certain embodiments, thede-scaling composition contains multidentate ligand(s) in an amount ofless than about 80 wt %, less than about 75 wt %, less than about 70 wt%, less than about 65 wt %, less than about 60 wt %, or less than about55 wt %. In some embodiments, the de-scaling composition containsmultidentate ligand(s) in an amount between about 10 wt % to about 20 wt%, about 10 wt % to about 30 wt %, about 10 wt % to about 40 wt %, about10 wt % to about 50 wt %, about 10 wt % to about 60 wt %, about 10 wt %to about 70 wt %, about 10 wt % to about 80 wt %, about 20 wt % to about30 wt %, about 20 wt % to about 40 wt %, about 20 wt % to about 50 wt %,about 20 wt % to about 60 wt %, about 20 wt % to about 70 wt %, about 20wt % to about 80 wt %, about 30 wt % to about 40 wt %, about 30 wt % toabout 50 wt %, about 30 wt % to about 60 wt %, about 30 wt % to about 70wt %, about 30 wt % to about 80 wt %, about 40 wt % to about 50 wt %,about 40 wt % to about 60 wt %, about 40 wt % to about 70 wt %, about 40wt % to about 80 wt %, about 50 wt % to about 60 wt %, about 50 wt % toabout 70 wt %, about 50 wt % to about 80 wt %, about 60 wt % to about 70wt %, about 60 wt % to about 80 wt %, or about 70 wt % to about 80 wt %.

In some embodiments, the de-scaling composition contains DTPA in anamount of at least about 10 wt %, at least about 20 wt %, at least about30 wt %, at least about 40 wt %, or at least about 45 wt %, (and/or insome embodiments, up to about 50 wt %, up to about 55 wt %, up to about60 wt %, up to about 65 wt %, up to about 70 wt %, up to about 75 wt %,up to about 80 wt %, or more). In certain embodiments, the de-scalingcomposition contains DTPA in an amount of less than about 80 wt %, lessthan about 75 wt %, less than about 70 wt %, less than about 65 wt %,less than about 60 wt %, or less than about 55 wt % (and/or in someembodiments, less than about 50 wt %, less than about 45 wt %, less thanabout 40 wt %, less than about 30 wt %, less than about 20 wt %, or lessthan about 10 wt %,). In some embodiments, the de-scaling compositioncontains DTPA in an amount between about 10 wt %, to about 20 wt %,about 10 wt %, to about 30 wt %, about 10 wt %, to about 40 wt %, about10 wt %, to about 50 wt %, about 10 wt %, to about 60 wt %, about 10 wt%, to about 70 wt %, about 10 wt %, to about 80 wt %, about 20 wt %, toabout 30 wt %, about 20 wt %, to about 40 wt %, about 20 wt %, to about50 wt %, about 20 wt %, to about 60 wt %, about 20 wt %, to about 70 wt%, about 20 wt %, to about 80 wt %, about 30 wt %, to about 40 wt %,about 30 wt %, to about 50 wt %, about 30 wt %, to about 60 wt %, about30 wt %, to about 70 wt %, about 30 wt %, to about 80 wt %, about 40 wt%, to about 50 wt %, about 40 wt %, to about 60 wt %, about 40 wt %, toabout 70 wt %, about 40 wt %, to about 80 wt %, about 50 wt %, to about60 wt %, about 50 wt %, to about 70 wt %, about 50 wt %, to about 80 wt%, about 60 wt %, to about 70 wt %, about 60 wt %, to about 80 wt %, orabout 70 wt %, to about 80 wt %.

According to certain embodiments, the de-scaling composition used toremove scale from a solid surface of the heat exchanger comprisesoxalate anions. Without wishing to be bound by any particular theory, itis believed that the combination of oxalate anions and at least oneother multidentate ligand exhibits a synergy that allows the combinationof these chemicals to remove much more scale than could be removed usingeither of the two chemicals alone. In particular, it is believed that,in some cases in which the oxalate anions have a geometry that isdifferent from the geometry of the other multidentate ligand, thedifferent molecular geometry exhibited by the oxalate anions mayincrease the rate of chelation/dissolution by interacting with scaleions that are not reachable by the other multidentate ligand or arereachable by the other multidentate ligand only to a limited degree.

According to certain embodiments, de-scaling can be achieved using arelatively low amount of oxalate anions. In some embodiments, thede-scaling composition contains oxalate anions in an amount of at leastabout 0.5 wt %, at least about 1 wt %, at least about 2 wt %, at leastabout 3 wt %, at least about 4 wt %, or at least about 5 wt %. In someembodiments, the amount of oxalate anions in the de-scaling compositioncan be less than about 20 wt %, less than about 15 wt %, or less thanabout 10 wt %. In some embodiments, the de-scaling composition containsoxalate anions in an amount between about 0.5 wt % and about 1 wt %,about 0.5 wt % and about 2 wt %, about 0.5 wt % and about 3 wt %, about0.5 wt % and about 4 wt %, about 0.5 wt % and about 5 wt %, about 0.5 wt% and about 10 wt %, about 0.5 wt % and about 15 wt %, or about 0.5 wt %and about 20 wt %.

In certain embodiments, the de-scaling composition used to remove scalefrom a solid surface of the water treatment system comprises oxalateanions and diethylenetriaminepentaacetic acid (DTPA). Without wishing tobe bound by any particular theory, it is believed that the combinationof oxalate anions and DTPA exhibit, in some instances, a particularlybeneficial synergy that allows the combination of the two chemicals toremove much more scale than could be removed using either of the twochemicals alone.

In some embodiments, the de-scaling composition used to remove scalefrom solid surfaces has a basic pH. For example, in some embodiments,the de-scaling composition has a pH of at least about 8, at least about10, at least about 12, or at least about 13 (and/or, in someembodiments, a pH of up to about 14, or higher). The pH of thede-scaling composition can be raised, according to certain embodiments,by adding hydroxide ions to the de-scaling composition. This can beachieved, for example, by dissolving one or more hydroxide salts (e.g.,potassium hydroxide, sodium hydroxide, or any other suitable hydroxidesalt) within the de-scaling composition.

It has also been found that the amount of water contained in thede-scaling composition can also impact the rate at which the formationof coordination complexes occurs. Thus, in some embodiments, thede-scaling composition is diluted with water. In some embodiments, thede-scaling composition contains water in an amount of at least about 10wt %, at least about 20 wt %, at least about 30 wt %, or at least about35 wt % (and/or in some embodiments, up to about 40 wt %, up to about 45wt %, up to about 50 wt %, or more).

The de-scaling compositions used to remove scale as described above canbe used to remove many types of scale, including many of the scalingsalts mentioned above or elsewhere herein (e.g., BaSO₄, SrSO₄, BaCO₃,and/or SrCO₃, and/or many of the scaling salts mentioned above orelsewhere herein). According to certain embodiments, the de-scalingcomposition is configured to remove scales that are most often formedwhen treating oilfield wastewaters, such as wastewater and producedwater from hydraulic fracturing operations. In certain (although notnecessarily all) embodiments, the de-scaling compositions used to removescale can be especially effective in removing strontium-containing scale(e.g., salts containing Sr²⁺ ions such as, for example, strontiumcarbonate, strontium bicarbonate, strontium sulfate, and strontiumbisulfate).

Example

As shown in FIG. 13, this example describes desalination system 1300,which comprises combined bubble column apparatus 1302, precipitationapparatus 1334, first heat exchanger 1336, second heat exchanger 1338,and cooling device 1340. Desalination system 1300 is configured toproduce 850 barrels of substantially pure water per day.

Combined bubble column apparatus 1302 comprises humidification region1304 and dehumidification region 1306 positioned vertically abovehumidification region 1304. As shown in FIG. 13, apparatus 1302 furthercomprises gas distribution chamber 1308 positioned vertically belowhumidification region 1304. In FIG. 13, gas distribution chamber 1308 isin fluid communication with apparatus air inlet 1310 and humidificationregion brine outlet 1312. In some cases, gas distribution chamber 1308comprises a liquid sump volume and a gas distribution region positionedabove the liquid sump volume. Humidification region 1304 comprises aplurality of stages 1314A-F that are vertically arranged above gasdistribution chamber 1308. Each of stages 1314A-F is coupled to a bubblegenerator and comprises a liquid layer and a vapor distribution regionpositioned above the liquid layer. As shown in FIG. 13, third stage1314C is fluidically connected to intermediate air outlet 1316, andsixth stage 1314F (e.g., the topmost stage of humidification region1304) is fluidically connected to humidification region brine inlet1318. Dehumidification region 1306 comprises a plurality ofvertically-arranged stages 1320A-F, each stage coupled to a bubblegenerator and comprising a liquid layer and a vapor distribution regionpositioned above the liquid layer. A liquid collection region positionedbelow first stage 1320A is fluidically connected to dehumidificationregion water outlet 1322, and sixth stage 1320F (e.g., the topmost stageof dehumidification region 1306) is fluidically connected todehumidification region water inlet 1324 and apparatus air outlet 1326.In addition, third stage 1320C is fluidically connected to intermediateair inlet 1328, which is fluidically connected to intermediate airoutlet 1316 through a gas conduit. Droplet eliminator 1330 and liquidcollector 1332 are positioned between humidification region 1304 anddehumidification region 1306.

In addition to combined bubble column apparatus 1302, desalinationsystem 1300 comprises precipitation apparatus 1334, first heat exchanger1336, second heat exchanger 1338, cooling device 1340, solid conduit1342, and liquid conduits 1344, 1346, 1348, 1350, 1352, and 1354.Precipitation apparatus 1334 is directly fluidically connected tohumidification region brine outlet 1312 and first heat exchanger 1336.First heat exchanger 1336, in addition to being directly fluidicallyconnected to precipitation apparatus 1334, is directly fluidicallyconnected to dehumidification region water outlet 1322, second heatexchanger 1338, and cooling device 1340. Additionally, second heatexchanger 1338 is directly fluidically connected to humidificationregion brine inlet 1318, and cooling device 1340 is directly fluidicallyconnected to dehumidification region water inlet 1324.

In operation, ambient air enters humidification region 1304 of combinedbubble column apparatus 1302 through apparatus air inlet 1310. Theambient air enters humidification region 1304 at a flow rate of 8330actual cubic feet per minute (acfm) and a temperature of 60° F. Thestream of ambient air flows upwards through each of stages 1314A, 1314B,1314C, 1314D, 1314E, and 1314F of humidification region 1304. Meanwhile,a stream comprising salt-containing water enters humidification region1304 through humidification region brine inlet 1318 at a flow rate of632 gallons per minute (gpm) and a temperature of 200° F. Thesalt-containing water stream flows in a direction substantially oppositeto the direction of the flow of the air stream (e.g., downwards througheach of stages 1314F, 1314E, 1314D, 1314C, 1314B, and 1314A ofhumidification region 1304). Each of stages 1314A-F is at leastpartially occupied by a liquid layer comprising the salt-containingwater. Accordingly, as the air stream flows upwards through the stagesof humidification region 1304, each of which is coupled to a bubblegenerator, air bubbles form and travel through the liquid layerscomprising the salt-containing water, which has a higher temperaturethan the air bubbles. As the air bubbles come into direct contact withthe salt-containing water of the liquid layers, heat and mass (e.g.,water vapor) are transferred from the salt-containing water to the airbubbles, and the air bubbles become increasingly heated and humidified.Within the vapor distribution region of each stage, heated and at leastpartially humidified air bubbles recombine to form an air stream that issubstantially evenly distributed throughout the vapor distributionregion. The substantially evenly distributed air stream may then passthrough a bubble generator coupled to the next stage and flow throughthe liquid layer of that next stage, becoming further heated andhumidified. When the air stream reaches third stage 1314C, at least aportion of the heated and at least partially humidified air stream exitshumidification region 1304 through intermediate air outlet 1316 at aflow rate of 8000 acfm and a temperature of 160° F. The remainingportion of the air stream continues to flow upwards through thevertically-arranged stages 1314D-F of humidification region 1304.

After flowing through stages 1314A-F of humidification region 1304, theheated, at least partially humidified air stream flows through dropleteliminator 1330 and liquid collector 1332 and enters dehumidificationregion 1306. The heated, at least partially humidified air stream flowsupwards through each of stages 1320A, 1320B, 1320C, 1320D, 1320E, and1320F of dehumidification region 1306. Meanwhile, a stream ofsubstantially pure water enters dehumidification region 1306 throughdehumidification region water inlet 1324 at a flow rate of 550 gpm and atemperature of 125° F. The substantially pure water stream flows in adirection substantially opposite to the direction of the flow of the airstream (e.g., downwards through each of stages 1320F, 1320E, 1320D,1320C, 1320B, and 1320A of dehumidification region 1306). Each of stages1320A-F is at least partially occupied by a liquid layer comprising thesubstantially pure water. Accordingly, as the heated, at least partiallyhumidified air stream flows upwards through the stages ofdehumidification region 1306, each of which is coupled to a bubblegenerator, heated, at least partially humidified air bubbles form andtravel through the liquid layers comprising the substantially purewater, which has a lower temperature than the heated, at least partiallyhumidified air bubbles. As the air bubbles come into direct contact withthe substantially pure water, heat and mass (e.g., water vapor) aretransferred from the air bubbles to the substantially pure water of theliquid layers, and the air bubbles become increasingly cooled anddehumidified. Within the vapor distribution region of each stage,cooled, at least partially dehumidified air bubbles recombine to form anair stream that is substantially evenly distributed throughout the vapordistribution region. In third stage 1320C, heated, at least partiallyhumidified air extracted from intermediate air outlet 1316 entersdehumidification region 1306 and joins the air stream flowing throughdehumidification region 1306. After flowing through each of stages1320A-F of dehumidification region 1306, the cooled, at least partiallydehumidified air stream exits combined bubble column apparatus 1302through apparatus gas outlet 1326.

As noted above, two liquid streams—a substantially pure water stream anda salt-containing water stream—flow through combined bubble columnapparatus 1302 counter-flow to the air stream. The salt-containing waterstream, which comprises water and at least one dissolved salt, entershumidification region 1304 of combined bubble column apparatus 1302through humidification region brine inlet 1318 and flows downwardsthrough each of stages 1314A-F of humidification region 1304 to gasdistribution chamber 1308. As the salt-containing water stream flowsdownwards through each stage of humidification region 1304, thesalt-containing water stream encounters air bubbles having a temperaturelower than the temperature of the salt-containing water stream, and heatand mass (e.g., water vapor) are transferred from the salt-containingwater stream to the air bubbles, thereby resulting in a cooled,concentrated salt-containing water stream. As the salt-containing waterstream flows through each stage of humidification region 1304, theconcentration of at least one dissolved salt in the salt-containingwater stream increases (e.g., due to evaporation of water). The cooled,concentrated salt-containing water stream then exits apparatus 1302through humidification region brine outlet 1312 at a flow rate of 593gpm and a temperature of 136° F. The cooled, concentratedsalt-containing water stream is then made to flow to precipitationapparatus 1334, and at least a portion of at least one dissolved salt inthe salt-containing water stream may precipitate within theprecipitation apparatus. The precipitated salt may be discharged fromsystem 1300 through solid conduit 1342. The remaining liquid portion ofthe salt-containing water stream exits precipitation apparatus 1334 as aprecipitation apparatus liquid outlet stream. In some cases, at least aportion of the precipitation apparatus liquid outlet stream isdischarged from desalination system 1300 through conduit 1344 at a flowrate of 593 gpm. Another portion of the precipitation apparatus liquidoutlet stream may remain in desalination system 1300. In some cases,additional salt-containing water may enter desalination system 1300through conduit 1346 at a flow rate of 25 gpm and a temperature of 60°F. The additional salt-containing water may combine with the portion ofthe precipitation apparatus liquid outlet stream remaining indesalination system 1300. The combined salt-containing water stream thenflows through conduit 1348 to first heat exchanger 1336, entering firstheat exchanger 1336 at a flow rate of 632 gpm and a temperature of 130°F. As noted above, first heat exchanger 1336 is also directlyfluidically connected to dehumidification region water outlet 1322, anda substantially pure water stream enters first heat exchanger 1336 at aflow rate of 575 gpm and a temperature of 170° F. As the salt-containingwater stream and substantially pure water stream flow through first heatexchanger 1336, heat is transferred from the substantially pure waterstream to the salt-containing water stream, producing a heatedsalt-containing water stream that exits first heat exchanger 1336 at atemperature of 160° F. and a cooled substantially pure water stream thatexits heat exchanger 1336 at a temperature of 140° F. The heatedsalt-containing water stream is then made to flow to second heatexchanger 1338 to be further heated. As the heated salt-containing waterstream enters second heat exchanger 1338 at a flow rate of 632 gpm and atemperature of 160° F. and flows through second heat exchanger 1338, aheating fluid also flows through second heat exchanger 1338 via conduit1350. Heat is transferred from the heating fluid to the heatedsalt-containing water stream to produce a further heated salt-containingwater stream having a temperature of 200° F. The further heatedsalt-containing water stream then returns to humidification region 1304of apparatus 1302 through humidification region brine inlet 1318 at aflow rate of 632 gpm and a temperature of 200° F.

In addition to the salt-containing water stream, a substantially purewater stream flows through combined bubble column apparatus 1302. Thesubstantially pure water stream enters dehumidification region 1306 ofapparatus 1302 through dehumidification region water inlet 1324 at aflow rate of 550 gpm and a temperature of 125° F. As the substantiallypure water stream flows downwards through each of stages 1320A-F ofdehumidification region 1306, the substantially pure water streamencounters bubbles of heated, at least partially humidified air, andheat and mass (e.g., water vapor) are transferred from the heated, atleast partially humidified air bubbles to the substantially pure waterstream, thereby resulting in a heated substantially pure water stream.As the substantially pure water stream flows downwards through each ofthe stages of dehumidification region 1306, the temperature of thesubstantially pure water stream increases. The heated substantially purewater stream then exits apparatus 1302 through dehumidification regionwater outlet 1322 at a flow rate of 575 gpm and a temperature of 170° F.After exiting apparatus 1302, the heated substantially pure water streamis made to flow through first heat exchanger 1336, where heat istransferred from the heated substantially pure water stream to theprecipitation apparatus liquid outlet stream (e.g., a portion of thecooled, concentrated salt-containing water stream that exited apparatus1302 through humidification region brine outlet 1312) to produce acooled substantially pure water stream. The cooled substantially purewater stream exits first heat exchanger 1336 at a temperature of 140° F.In some cases, at least a portion of the cooled substantially pure waterstream exits desalination system 1302 through conduit 1352 at a flowrate of 25 gpm and a temperature of 140° F. In some embodiments, atleast a portion of the cooled substantially pure water stream remains indesalination system 1302 and is made to flow through conduit 1354 tocooling device 1340. The cooled substantially pure water stream enterscooling device 1340, which may be an air-cooled heat exchanger, at aflow rate of 550 gpm and a temperature of 135° F. As the cooledsubstantially pure water stream flows through cooling device 1340, thestream is further cooled to a temperature of 125° F. The further cooledsubstantially pure water stream then returns to combined bubble columnapparatus 1302, entering dehumidification region 1306 of apparatus 1302through dehumidification region water inlet 1324 at a flow rate of 550gpm and a temperature of 125° F.

While several embodiments of the present invention have been describedand illustrated herein, those of ordinary skill in the art will readilyenvision a variety of other means and/or structures for performing thefunctions and/or obtaining the results and/or one or more of theadvantages described herein, and each of such variations and/ormodifications is deemed to be within the scope of the present invention.More generally, those skilled in the art will readily appreciate thatall parameters, dimensions, materials, and configurations describedherein are meant to be exemplary and that the actual parameters,dimensions, materials, and/or configurations will depend upon thespecific application or applications for which the teachings of thepresent invention is/are used. Those skilled in the art will recognize,or be able to ascertain using no more than routine experimentation, manyequivalents to the specific embodiments of the invention describedherein. It is, therefore, to be understood that the foregoingembodiments are presented by way of example only and that, within thescope of the appended claims and equivalents thereto, the invention maybe practiced otherwise than as specifically described and claimed. Thepresent invention is directed to each individual feature, system,article, material, and/or method described herein. In addition, anycombination of two or more such features, systems, articles, materials,and/or methods, if such features, systems, articles, materials, and/ormethods are not mutually inconsistent, is included within the scope ofthe present invention.

The indefinite articles “a” and “an,” as used herein in thespecification and in the claims, unless clearly indicated to thecontrary, should be understood to mean “at least one.”

The phrase “and/or,” as used herein in the specification and in theclaims, should be understood to mean “either or both” of the elements soconjoined, i.e., elements that are conjunctively present in some casesand disjunctively present in other cases. Other elements may optionallybe present other than the elements specifically identified by the“and/or” clause, whether related or unrelated to those elementsspecifically identified unless clearly indicated to the contrary. Thus,as a non-limiting example, a reference to “A and/or B,” when used inconjunction with open-ended language such as “comprising” can refer, inone embodiment, to A without B (optionally including elements other thanB); in another embodiment, to B without A (optionally including elementsother than A); in yet another embodiment, to both A and B (optionallyincluding other elements); etc.

As used herein in the specification and in the claims, “or” should beunderstood to have the same meaning as “and/or” as defined above. Forexample, when separating items in a list, “or” or “and/or” shall beinterpreted as being inclusive, i.e., the inclusion of at least one, butalso including more than one, of a number or list of elements, and,optionally, additional unlisted items. Only terms clearly indicated tothe contrary, such as “only one of” or “exactly one of,” or, when usedin the claims, “consisting of,” will refer to the inclusion of exactlyone element of a number or list of elements. In general, the term “or”as used herein shall only be interpreted as indicating exclusivealternatives (i.e. “one or the other but not both”) when preceded byterms of exclusivity, such as “either,” “one of,” “only one of,” or“exactly one of” “Consisting essentially of,” when used in the claims,shall have its ordinary meaning as used in the field of patent law.

As used herein in the specification and in the claims, the phrase “atleast one,” in reference to a list of one or more elements, should beunderstood to mean at least one element selected from any one or more ofthe elements in the list of elements, but not necessarily including atleast one of each and every element specifically listed within the listof elements and not excluding any combinations of elements in the listof elements. This definition also allows that elements may optionally bepresent other than the elements specifically identified within the listof elements to which the phrase “at least one” refers, whether relatedor unrelated to those elements specifically identified. Thus, as anon-limiting example, “at least one of A and B” (or, equivalently, “atleast one of A or B,” or, equivalently “at least one of A and/or B”) canrefer, in one embodiment, to at least one, optionally including morethan one, A, with no B present (and optionally including elements otherthan B); in another embodiment, to at least one, optionally includingmore than one, B, with no A present (and optionally including elementsother than A); in yet another embodiment, to at least one, optionallyincluding more than one, A, and at least one, optionally including morethan one, B (and optionally including other elements); etc. In theclaims, as well as in the specification above, all transitional phrasessuch as “comprising,” “including,” “carrying,” “having,” “containing,”“involving,” “holding,” and the like are to be understood to beopen-ended, i.e., to mean including but not limited to. Only thetransitional phrases “consisting of” and “consisting essentially of”shall be closed or semi-closed transitional phrases, respectively, asset forth in the United States Patent Office Manual of Patent ExaminingProcedures, Section 2111.03.

In cases where the present specification and a document incorporated byreference, attached as an appendix, and/or referred to herein includeconflicting disclosure, and/or inconsistent use of terminology, and/orthe incorporated/appended/referenced documents use or define termsdifferently than they are used or defined in the present specification,the present specification shall control.

What is claimed is:
 1. A method of removing scale, comprising: providinga desalination system comprising a plurality of desalination units,wherein two or more desalination units of the plurality of desalinationunits are heat exchanger-containing desalination units that eachcomprise a humidifier, a dehumidifier, and a first heat exchangerfluidically connected to the humidifier; flowing a first fluid streamthrough a first fluidic pathway of the first heat exchanger of each heatexchanger-containing desalination unit; flowing a second fluid streamthrough a second fluidic pathway of the first heat exchanger of eachheat exchanger-containing desalination unit; measuring a firsttemperature of each second fluid stream downstream of the first heatexchanger; determining an average first temperature of all the firsttemperatures measured in the measuring step; identifying at least onefouled first fluidic pathway characterized by a first temperaturemeasured in the measuring step that differs from the average firsttemperature by greater than 10% on the Kelvin scale; and selectivelyflowing a de-scaling composition through only the at least one fouledfirst fluidic pathway.
 2. A method of removing scale, comprising:providing a desalination system comprising a plurality of desalinationunits, wherein two or more desalination units of the plurality ofdesalination units are heat exchanger-containing desalination units thateach comprise a humidifier, a dehumidifier, and a first heat exchangerfluidically connected to the humidifier; flowing a first fluid streamthrough a first fluidic pathway of the first heat exchanger of each heatexchanger-containing desalination unit; flowing a second fluid streamthrough a second fluidic pathway of the first heat exchanger of eachheat exchanger-containing desalination unit; measuring a first flow rateof each second fluid stream downstream of the first heat exchanger;determining an average first flow rate of all the first flow ratesmeasured in the measuring step; identifying at least one fouled firstfluidic pathway characterized by a first flow rate measured in themeasuring step that differs from the average first flow rate by greaterthan 10%; and selectively flowing a de-scaling composition through onlythe at least one fouled first fluidic pathway.
 3. The method of claim 1,wherein the first fluid stream is a salt-containing water stream.
 4. Themethod of claim 3, wherein the salt-containing water stream comprisesseawater, brackish water, flowback water, water produced from an oil orgas extraction process, and/or wastewater.
 5. The method of claim 1,wherein the second fluid stream is a heating fluid stream.
 6. The methodof claim 5, wherein the heating fluid stream comprises water.
 7. Themethod of claim 1, wherein the first temperature and/or first flow rateof each second fluid stream is measured at a liquid outlet of the secondfluidic pathway of the first heat exchanger.
 8. The method of claim 1,further comprising flowing a first fluid stream from a common source ofthe first fluid stream to the first heat exchanger of each heatexchanger-containing desalination unit.
 9. The method of claim 8,wherein the common source of the first fluid stream is a central feedtank.
 10. The method of claim 1, further comprising flowing a secondfluid stream from a common source of the second fluid stream to thefirst heat exchanger of each heat exchanger-containing desalinationunit.
 11. The method of claim 10, wherein the common source of thesecond fluid stream is a boiler.
 12. The method of claim 1, furthercomprising measuring a first temperature of each first fluid streamdownstream of the first heat exchanger.
 13. The method of claim 12,wherein the first temperature of each first fluid stream is measured ata liquid outlet of the first fluidic pathway of the first heatexchanger.
 14. The method of claim 12, further comprising selectivelyincreasing a flow rate of a second fluid stream flowing through a firstheat exchanger of a heat exchanger-containing desalination unit if thefirst temperature of the first fluid stream flowing through the firstheat exchanger falls below a threshold temperature.
 15. The method ofclaim 14, wherein the increasing flow rate step is performed by anautomatic feedback control system.
 16. The method of claim 1, furthercomprising measuring a second temperature of each first fluid stream oreach second fluid stream upstream of the first heat exchanger.
 17. Themethod of claim 16, wherein the second temperature is measured at aliquid inlet of the first heat exchanger.
 18. The method of claim 16,further comprising determining a relative standard deviation of all thesecond temperatures of the first fluid streams or a relative standarddeviation of all the second temperatures of the second fluid streams,wherein the relative standard deviation is about 50% or less.
 19. Themethod of claim 18, wherein the relative standard deviation is about 20%or less.
 20. The method of claim 1, wherein the scale comprises a saltcomprising Mg²⁺, Ca²⁺, Sr²⁺, and/or Ba²⁺. 21-38. (canceled)